Hey everyone!
I just wanted to write this discussion for any of those that are having trouble with the game :) I've read a lot in the comments about people stopping because of difficulty and I'm hoping to make it easier for everyone to enjoy! Although I won't completely in-depth with everyone you have to do, just what I've seen people most commonly stuck on. Also, as I'm writing this at 2:30 AM after just beating the game, I'm more focused on pointing people in the right direction than exactness or accuracy (mostly for terminal), so if some things are slightly off I apologize, but they will still point you in the right direction.
As this is a walk-through of sorts, expect spoilers

Starting the Game:
Just subscribe to the mod, and as long as SOMA is downloaded it'll automatically install too (at least it did for me). When you hit "Play" choose "Play mod" and then "custom content". The custom story should start from there :)

Computer room:
DO NOT TRY TO OPEN THE HATCH YET.
When using the terminal, type "Help" to see a list of commands
Open the archives and read all of the files (I highly recommend actually reading as the lore is both important later and a good story). You will get notifications saying your permissions have been updated, keep using the "list" and "open" commands to view and read the new documents. A new document will be added every time until the last one, which has a completely different format than the others (and is a poem).
When you get to this document, you'll see it says your permissions have been updated again, but no new document has appeared.
Use the "back" command to go back to the root directory. Then go to the other folder (forget what it's called, but it's the only other one) and use "open hatchdoor.sh"
The hatch door will be quite heavy, so don't worry if it takes a second to open it, just keep trying and enter the tunnel as soon as you can.

Room with ladder/monster:
When you enter a room and see a broken ladder, notice the conveyor belt in front of you (don't do anything with it rn, but it'll help later on).
Turn right and enter the airlock room, remove the pipe on the ground. which is the "invalid metal object", from the room so you can use the airlock.
Once you get into the next room, you need to find a fuse in the storage, plug it into a fuse box, and find the ladder.
Storage is straight ahead from where you entered the room, although a little hidden behind a wall to the left. There is an electronics box with fuses in it on the wall, you only need to get one.
The room you need to put the fuse in is to the right of where you entered. Basically hug the wall until you find a room with two doors and, upon entering, your character will pull out the fuse so you know it's the right room. The fuse box should be glowing.
The ladder will be in the very back of the room (DO NOT TRY TO CARRY IT ALL THE WAY BACK, remember the airlock room doesn't allow metal objects), farthest point from where you entered. Next to it will be a conveyor belt with a switch to the left that says "destination required". Go to the room a little farther down (if you're entering from the right side after using the fuse), and go onto the computer. You only have one destination to choose from, which makes it pretty easy.
Select that destination, go back, put the ladder onto the conveyor belt, use the switch, and run back to the room with the broken ladder. Once you attach the ladder piece to the rest of the ladder you'll be all set to go up.
Note about the monster: At least in my experience, the monster is very 'passive'. It moves chaotically sometimes, but I've had times where it has 'seen' me or I've sprinted around rooms and it never chased or caught up to me. I only died once when I was trapped in a corner and was praying to god it didn't get closer XD but even then it took a long time relatively speaking. Not to mention it won't kill you the first time it gets you either, so don't worry too much about the monster if you don't think you can get past it.

Room with light/crane:
DO NOT GO INTO ANY LIGHT (in case you didn't read the lore earlier, light = bad, it's how the SCP kills people and turns them into the monster you were being chased by earlier)
Go left, up the stairs, and you'll see an inoperable crane lever. However you will also see a bridge connected to the same elevated platforms. Go across the bridge, into the room, turn on emergency shutters (so you don't accidentally die from walking backwards) and turn on the crane. Go back to the crane, and you're basically just trying to align the crane so that it creates a shadow across the light for you to walk across.

The rest is hopefully pretty easy, or at least not as many people seem to be having trouble with. If you get stuck someone just let me know and I can try to help.
P.S. Sorry if there are any typos, I'm sleep deprived XD