I'm not too much of a fish person; I've never really strayed from the ones that are supposed to be easy to care for so I know some of those well I guess lol. The following groups of fish are generally pretty easy to take care of in terms of feeding and hardiness and don't have much worry in terms of aggression if you stock cautiously:
Clowns, particularly captive-bred options that are still wild-type rather than designer. Obviously maroons and tomatoes are nastier and bigger, but Ocellaris and Amphiprion are pretty common starter species.
Most of the commonly seen gobies and blennies.
The more commonly seen cardinals like PJs and Bangais. There are also captive-bred options for some cardinals.
I have never kept tangs myself, but I would not put them in the same hardiness category as a lot of other good beginner fish since they are very ich-prone by comparison. Getting an ich-free tang without a quarantine tank seems like a less than trivial task from the amount of complaints I hear. A 90gal should easily house one of the smaller tank species, but if your main worry is that the fish is hardy while you get your feet wet, then I would stick to maybe a clown pair and some gobies for a bit until you're comfortable with things.
Damsels are also hard as nails, and some of the nicer species are easily stocked with other fish like cardinals and blennies. I've also seen a lot of successful community tanks of similar size to yours that have a damsel somewhere in the mix. However, even though many damsels are probably the hardiest thing you can possibly get, it's usually considered a bad idea to start with one, since that's how a lot of aggression problems start: the damsel gets established first and then tries to defend the entire tank. Personally I love damsels for their hardiness and character, but clowns are easier to deal as a starter fish since they have smaller territories.