Hi, and welcome to the forum, you should find many answers in the tutorials in the scriptorium, start with the categorized index:
https://forums.totalwar.org/vb/local_links.php?catid=70

https://forums.totalwar.org/vb/showthread.php?t=63904 about changing a roman faction might be helpful

1. How do I change the model of the guy of my faction on the campaign map? Like when you have an army marching, you have a model representing that army depending on your faction but I'd like to know if I can edit that?
the text files for that are descr_character.txt and descr_model_strat.txt
you can change his colour by editing the texture in any graphics program that will take the Nvidia dds plug-in. To change the model shape though you need 3dsmax which is an expensive 3d modelling program. If you have model and texture from a mod/faction that you want to swap in you can just alter the text files.
2. How do I change the names of the faction generals so that no general ever born or betrothed have an Egyptian name? (I am editing egypt)
Egypt has its own set of names in descr_names.txt so you can change all of those, if you change them you must make sure you also change them in descr_strat.txt and in background script if you have one. Any new names added to the game must also go in data/text/names.txt or the game will CTD.

3. How do I change the model of the buildings? I downloaded a mod but I don't want to apply the WHOLE mod, I just want to use a bit of it. (NB: Mod is now dead) so I want to apply the buildings into my campaign.
If you want to release your mod publicly you may still need permission from the creator of the building, even if mod is apparently abandoned, unless it said things were free to use. To add a battlemap building you need to get its .item included in your items.db file, see https://forums.totalwar.org/vb/showthread.php?t=60818 for method and helpful extracts of vanilla files by Alpaca, to enable game to reconstruct the db file.