I agree with the advice about starting a few characters and taking them to 20. However, give your preference for tanking and self-healing, I think a Guardian would be more up your alley. A Captain does a bit of everything - heals, has a pet, buffs, debfuffs, tanks, and a bit of dps. Based on the make-up of a group, they could go from being a secondary healer to dps to tank. Very often in battles they won't be focusing on damaging the enemy (more focused on healing and providing the right support). The only self-heals they have are from a summoned "pet" (their hearld) and from a defeat-response skill (once they defeat an enemy they can get some health regen).
The guardian is much more adept at tanking, and also has more self-heals. I do play a captain, and never played a Guardian (as tanking doesn't interest me), but based on what you described for your prefered role, I'd say Guardian is what you'd likely like.