I'm not sure how much under the cap Thunder is, but I guess they have some money left.
Take Luke back, he can play backup pg much better then Earl, get pick 10-15 for hm, I'm sure there's a second rounder lying around. Draft Derozan/Blair, depending on 1st pick.
Watson can stay, but I'm afraid Westbrook will play to much sg, or he can be dealt with SA 1st for position of need, if thee's any left.
My ideal lineup after the draft

Westbrook, Ridnour
Sefolosha, Weaver, DeRozan
Durant
Green, Monroe
Krstic, Collison
deep, very talented team
ps: i guess memphis and maybe even Detroit might have the same idea