Want to come back and bring my buddies, not sure what the best way to do it is.

As the title says, I grew up playing vanilla and played through cataclysm, but it's been a long time since I have done anything related to wow. Should I try to reactivity my old account? Or set up a new one? My old account had multiple toons in what was good raid gear and everything else you'd expect. Or should I just start over completely? I'm kind of torn. My buddies are in the same position. How much money am I looking at spending to deactivate/catch up on all expacs?