Questions about mods adding classes

New classes aren’t hard to do, but they are pretty tedious. I think a great start for what you want to do is to get the 3 of them working properly into the promotion tree where you don’t have any issues with the clothing, tallisman, etc.
Step 2 would be limiting what each class can do, and maybe overriding existing classes. I dug through all the ai packs that determine what abilities each class has (at least the ones that existed at the time, I don’t know if there are any new ones since) and documented it [Collective Knowledge] Class Abilities (Jobs).

You can also read through Scholar Mod - Revived! (Semi-transparent features fixed) where I was helping @fantasyworm to see just how tedious it can get, and all the small little details that are easy to miss when creating a new class. I’m sure he/she will be probably also be able to chime in and help out when/if you start running into walls. Just remember, the error log is your best friend.