Newbies, start here.
Yes, of course: Every quality collection ought to include Rumours. Bet yours already does. True devotees also would/should want pressings of the self-titled ‘75 LP, probably Tusk, either of the ‘80s titles or both, plus at least a representative platter for both the Bob Welch era (I vote Bare Trees) and the foundational Peter Green years (Then Play On is tops, although there’s a Greatest Hits for that phase as well, from ‘71).