a community is intended to be like, a single city/village/whatever. You can earn fellowship with multiple Elven communities, absolutely - what matters is you saved each from danger and earned their favor.
As for how many Fellowships you earn, in my games its been about 4-6. You don't need a ton of 'em, each one is fairly powerful and by that point everyone's got a Destiny playbook, which is really about when "go take down the overlord" feels right.