Well, I mean, Eldar are generally humanoids, as are most of the races in the 40k universe, so technically you could just use your typical human statistics, and just put an eldar twist on them, since Eldar warriors take a long time to train, and mainly use projectile weapons (Shuriken Canons for the win) Instead of homeworld per say, you could graft on from Dark Heresy and instead use craftworlds. (I've sadly only played Dark heresy, however if I'm allowed, i'd surely use the other systems if given the information and guides to each set. A good plotline would probably be something do with the webways, since that one chaos guy got into the place, Ahriman I think his name is, perhaps the story is that you must stop him, and some things go bad with the webway eithier transporting some Nids, or unleashing some daemons left over from the Horus Heresy era (Since I did read up and Chaos did ambush them there.) Or perhaps some Tzeench daemons decide they want to mess up some poor Eldar whilst they are inside, and bippity boppity boo, some random warp stuff happens, maybe some transports to an uncivilized, yet hostile world teeming with life? TL:DR I'd love to join and do shit with the Eldar. Eldar and the Guard happen to be my bae.