Hi there /u/Erroron. I've been learning semi-advanced commands for quite a while now. I've learned how to use /scoreboard to its almost full potential and I finally understand JSON. Thus, I am willing to help beginners like you as best as I can.
But that's enough about me. Let's talk about you. Note that I will answer your questions down here, but first, please take into consideration that people new to commands and mapmaking should not venture so far into the advanced domains this quickly. That being said, I am willing to guide you throughout the wonderful, wonderful word of command blocks and try to teach you all I know slowly and steadily, so you can understand everything and easily make progress. Because that's the problem with a lot of YouTube tutorials. They are very vague and very hard to understand by newbies.
That being said, again, I will also answer your three questions since that is the main purpose of the post.
Possible and easy, but only by making it a 100% chance. That AFAIK.
Not AFAIK, again.
Nope. Impossible, at least currently.