Hi, everyone. I was greatly inspired by your project. I would really like to help you, but I am a real noob in programming. Still I want to learn. Of course, I will not be able to do something at once, but would like to participate in future projects. So my question is, where and what should I find to start learning? (At least to understand what you do on the base of Heroes 3) Thank you.
Buy C for dummies (realy good book), read it, understand it. Buy C++ for dummies, read it, read it twice, understand it. Try to write an own small project. Try to use a SVN (subversion) for it. Try to use cmake as building system for it. Try to use a lib like boost in it.
This will take a lot of time. When you realy managed to do it, I think you try to start to work on something this big.
If not, I think some graphic stuff or something can be used in VCMI too 
No idea about English C++ books. But you definitelly to get one that suits you and start learning.
If you have no former experience with programming, you may try some simple scripts in other games, bash scripts for file management or whatever you find interesting. It’s better to use even little skills in application you find useful, it’s always motivating.
Why not go back in time to the day 1? It’d be even quicker. 