1. A single sheet with everything works best, as it consumes the least amount of memory and is the standard way of doing it in this game. I reckon in the current state it's like 6 general icons for the basic resource buildings + their construction icons and max 9 icons for the special ones, which of course you could distill to 1 in which case the total is 13 icons. Perhaps preparing a few extra (ie. Shipyard) could prove to be handy.
1 sheet can hold up to / over 100 icons depending on its size so... If you don't make race-specific icons for each and every "Build a Farm" etc. then 1 sheet should suffice.
Construction icons seem to be unique like the ability icons, but they are not as relevant as the ability icons themselves so I leave it up to you to decide whether you want to make them or not.



2. I believe I can make do with just the .dds. It seems making the .clb file is basically part of integrating the file into the mod itself so that part falls on me. You could include the .png file for quick reference, doesn't hurt.
It should be fairly simple...
The specifics of icon creation are detailed on page 55 of the "Modding Guide v1" that you should be able to find online. If you can't find it I can send it to you! For now here are two quotes regarding the sizes:

"You will want to draw your icons precisely inside the circles, then hide all the template elements (circles, squares, numbers, text, etc.). When you want to have more than ten icons, you will have to create a bigger image, ensure that it’s width and height are both powers of two (256x256, 512x512, 1024x512. Etc). Each icon is 96 x 96 pixels in size."

"As a final note, although “Large (96)” icons are the most commonly used type, they are not the only type used by the game. Some resources will use Extra Large icons (which are 128x128 pixels) while others may use small icons (64x64 pixels)"

The circles refer to the ones in the template. You could be able to find the template online, but I think most of the links are long dead.
I do have an icon sheet in .jpg format that you could use as a base though.
In our case the ability icons are 96x96, but the icons that are used while the buildings are under construction are 128x128.



3. As for the content I'd say I like your idea of mix & match. Staying within the art-style of the game must also be easier that way. As long as it isn't directly stolen content from elsewhere, almost anything that works is ok on my part. Artists choice in the end.



Here is an easy-to-find discussion on the topic of icons. You may have already seen it
http://aow.triumph.net/forums/topic/icon-creation/

Main point I figure from that is perhaps this:
"When you import the icon texture, make sure you change the following in the texture’s settings:

a. Streaming Enabled = false
b. Quality Modifier = Increase (+1 Mipmap)
c. Quality Level Min = 100"

in addition to detailing how to make icons that stick out.

Another discussion, jumping from the previous one:
http://aow.triumph.net/forums/topic/icons-and-graphics/

From which I believe this is the important bit:
"Yes, you can use GIMP for .psd files.
I think there is a GIMP plugin for creating .dds files too.
Or just save your creation as png/jpg and convert them with DirectX Texture Tool (dxtex.exe)."

I put these together yesterday as a preview:
https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=1394496503

Did not have time to figure out the formatting yet; chose to start with the content using what time I had. It's just a png at the moment, though I did find the .dds plugin for gimp, so I could use that to convert it, once its in final form.

All 128x128 for now. Racial building aren't included and variant building for the same resource (i.e. forge vs dungeon vs quarry) aren't given special treatment; there is just a "low", "average", "high" and "excellent" image for each resource + the vault of knowledge and the shipyard.

Anyway, I should have something more polished in a while, but wanted to post this and see what you thought.

Aaaand after making these, I finally found the assets are for the icons that actually go with each structure in the game. I so infrequently click on resource structures on the strategic map I'd forgotten that they all already have icons that show up in the game, so I used substitutes. Feel kinda dumb, even though the substitutes still look pretty decent. Anyway, having most of those source icons makes it way easier. A few structures (like the ziggurat) I still can't figure out what library their icon is in but I can extract them from screenshots.

Ok, new preview sheet:

https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=1395330390

Aha!
Success!
(I think?)
https://www.dropbox.com/s/2bttve72xrvzcqv/BuilderIcons.clb?dl=0

From the preview everything looks great. I like the style.

I checked out the .clb with the editor just now, everything seems to be in order from a glance. I haven't tested attaching it to anything in the mod yet. That'll have to wait as I need to go sleep right now (5:30 am). I'll test them out once I wake up.

Nice work. And thank you for doing this.

Ingame they appear as black boxes. This problem seems to be the same as the one in the first link I pasted here: having no alphas in the file.
Link in question: http://aow.triumph.net/forums/topic/icon-creation/

Here's what he said about it:
.....
1. You should see the Channels tab next to the normal Layers tab, select it..

2. ..and see that your alpha channel is empty

3. Go back to Layers view and make a selection around the unit (the background of the circle needs to masked out as well as the playercolours will show up here)

4. Go to channels and click the button shown in the picture, this will make “Alpha 2” , delete “Alpha 1”

5. Hurray, it’s masked properly now 🙂

EDIT: looks like you were on the right path when looking at the photoshop file (assuming you made “Test 1”) hopefully this is useful to other people too
.....

Otherwise these seem to work nicely for both contruction and ability icons, I would need them in both 96x96 and 128x128 formats though.

Ok, cool. I'll try to figure out how to do the alpha-channels thing and make 2 versions with 96 and 128 sizes.

Ok....... https://www.dropbox.com/s/2bttve72xrvzcqv/BuilderIcons.clb?dl=0
Same link as before, 2 textures with 96 and 128 sizes, including a draconian watchtower, and with an alpha channel. Fingers crossed.

Hey, I tested it. And I was almost going waste your time by posting something about how they dont work, but luckily I realized to fix the texture settings in time...

So. They work. Excellent work! However...

The icons indeed are in a grid with boxes of 96x96 and 128x128 but the circles within them seem to be much smaller, so the icons currently are pretty out-of-place as they are bigger. For the 96x96 icons it seems they are actually circles with 76-pixel diameter with the edges going darker and darker. I don't know the exact size for the 128x128 ones. I'd imagine similarly smaller...

With the current sizes, the selection circles (when selecting what to build) are hidden.

Sorry I didn't realize this beforehand... I can imagine how annoying it is to resize these as the smaller icons within would lose shape etc... But can I ask you to do that please? At least for the 96x96 ones?

As a separate suggestion... if you have the smaller icons indicating the production amounts as a separate layer, to have those "stick out" of the circle. If not, that is ok.


So. They are usable now, but if you feel like resizing them, that'd be great!

http://aow.triumph.net/wp-content/uploads/2015/09/Icons.jpg

This image should help with the sizing... If you can't open it you have to login to triumph first.

Evidently I dont know how to do that image link thing so here's the link to my artwork page in which I only have the pictures on how the icons look right now...

https://psteamcommunity.yuanyoumao.com/profiles/76561198046237858/images/

Heh, ok cool. Nice to know that I actually have the whole 96 or 128 to work with but am just expected not to use it all most of the time. :) Love the idea of having the production icons sticking out of the circle, I'll do that.

https://www.dropbox.com/s/50vs0ygzxvi132a/BuilderIcons2.clb?dl=0

This time for sure!
(preview: https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=1397472723 )

Nice job! I will update the mod with these as soon as I can. I have added them to the Dwarf race as a test, but right now I need to sleep. I'll include you as a contributor. You can check out how they will look ingame from my artwork page:
https://psteamcommunity.yuanyoumao.com/profiles/76561198046237858/images/?appid=767

Thank you for going out of your way to make these. This is great.

EDIT: If you check out the third picture you can see the construction icons aren't quite right, but I don't have the correct dimensions for them at the moment so well... It's no big deal. At least the build-menu and ability page are looking great.

EDIT2: Hmmm... It might be the 128s are just 128 hmm I am not sure. What is their current size in what you made?

Ok, yeah "constructor icons" do fill the whole circle, but ability icons don't. Cool. I should have noticed this in the game's own assets. But luckily I still have the icons that fill the circle.

https://www.dropbox.com/s/e4ucp6scg1l76az/BuilderIcons3.clb?dl=0&m=
This clb has the 128 size icons from the first iteration that fill the whole circle and the 96 size icons from the 2nd that don't.

Nothing good ever got made without being iterated on. :)