I'm considering using a couple custom heroes made with the rules provided in this site (the main reason is I wanted a character with 6 movement points, and since I havent tested it yet I dont even know if it's useful)

the abilities described in the documentation don't include new abilites that can be found in the expansions, so my question would be, how would you rate in points a regeneration 1 ? and how about a regeneration 2? is that ok to rate them 0-3 and 4-8 respectively?
I have to make sure it's balanced or it won't be fun to play

There's an official hero in the Tomb of Ice expansion with a speed of 6 (Okaluk & Rakash).

The official build-your-own-hero rules are not very good, and in particular the costs of the abilities are ridiculous. There are some "0-3 points" abilities that are arguably better than some other "9+ points" abilities, and some abilities get a huge boost each time you go up a tier and others get barely anything. So asking how many points some new ability should cost in this system is fairly pointless; you could get almost any answer depending on which of the existing abilities you choose to compare them to.

I've designed my own hero editor that you may find interesting. It's a lot more flexible than the official rules, and includes a lot more abilities.