Once you are out of a gravity well as a civ, why would you bother with them economically aside from tourism? Unless we get antigravity, or loop launch / space elevator / space hook sized planetoids (I think Mars is the practical limit of space elevators last I looked).

Red dwarfs appear ideal. Very long lived, and there do seem to be planets and asteroid material in them. A globular cluster of mostly red dwarfs would be an ideal long-term place for an "interstellar" civ. The stars drift as close as 1/3 light year.

Look at what some of the projected mineral yields of asteroids are. And comets can probably get you other element mixes as needed.

Yes, I think Lithium will be be available artificially with some form of fusion. Or you capture solar wind material perhaps.