yeah something like that,

Town halls build peasants, unless you want spearmen.
vikings don't have a stable i believe, so scout cav can be recruited there.

Start with all the buildings already constructed and every unit unlocked, except the blacksmith.
Barracks unlocks every melee unit that's a foot soldier.
Archery unlocks every ranged unit that's not mounted.
stable unlocks every mounted unit melee or range.
Siege will remain in the blacksmiths shop like catapults and the grenadier for the moops.

Tiers- The three tiers in vanilla ancestors that is used upgrade your keep can represent the armor/grade of your troops or something.

So every time you build a new troop they'll have a tier 2 silver upgrade or a tier 3 gold. For existing troops you can bring them back to rearm them with the new upgrade, it should cost less then buying a new unit.

Upgrades for soldiers like veteran/or a longbow upgrade for example can remain inside the correlating buildings they are recruited in.

Not sure if this is a little ambitious of me asking this of you, but in the end I cant and who will so I'm very thankful of this.

It's about knowing what we want. That must be ambitious ;-). So that we can check/test it step by step to see if we can do it that way. We will not be able to convert everything, perhaps only a little, as we planned. You must be aware of this and you must not be too disappointed.

So I will tonight (Switzerland Time ;-) ) when I can restore the default setting. Then create a new test mod, make small changes and invite you and others as testers. Then we can always test it first before releasing the mod.

Sounds cool, thanks for the invite chief.