First of all, I'd like to recommend reading Bluefire's idea for a mod, that it's currently under construction:https://docs.google.com/spreadsheets/d/1...t#gid=933636169
As you can see, the game can be pretty much reconstructed and all the current functionalities can be deactivated or changed.
Basically, everything you said is doable. Some stuff would be easily manageble through stats editing and simple tweaks. Other things would heavily rely on scripting, needing complex logic and a lots of code. It's all up to the amount of work you're intended to put on the mod.