I seriously squealed in real life over this XD I've been slowly chipping away at a game that involves combat and have been wracking my brain trying to figure out how to make it work with the 3d6D system (especially since my partner's so much into the crunch and stats and such). I LOVE the idea of using the third dice for damage/heals! Hope you don't mind if I use it c.c
Yeah, definitely use the system as a base and build up as much as you want! There's a reason one of the rules I had was to hack it as much as you want :D While it's made to be a simplistic system, I think it would be great to see how many different ways it could fit with other systems and everything.
I think that last thing you thought of could be really cool. It sounds way too powerful at first, but I think the third die could be a great way to keep things balanced. There are things that might not need a third die, but of course GM could always say "Dial it back a bit there".
All in all I'm really digging the Eousi and now I want to revisit Hotshots XD It sounds like this is going to be great!