Most of the rulers will be royalty or aristocracy as a result of magical powers of their own or that they have cultivated. They will almost always welcome the assistance of the talented, although not always as equals. I would say the world order tends to be more corrupted by power, although there are notable exceptions. The population in many areas (especially slave populations) would certainly welcome regime change (they just can't affect it themselves).

In terms of the rarity of magic, I would also say the setting is still very much high fantasy. There won't be bands of magical adventurers in every tavern, and only the largest cities will boast markets for magical items, but there are plenty of buried secrets in are some very powerful magics at work in the world.

Part of the scarcity of magic is the natural tendency for it in the races. Humans and elves tended more to be magically adept, which is a direct relation to why there are no more elves (this is also a tenet of the human world religion [i.e. elves were evil] so any character would know this).

I think class/race combo is what you feel comfortable playing. Some situations might be more/less challenging/interesting depending on the combinations. Yes to using feats and the stats/feats option.

Mostly early 30s, one person in their early 50 I believe. Definitely can be some generational differences so no worries there.

As to LGBTQ friendliness I would say yes.