Crowder, Smart, and the BKN pick are 3 of the C's 5 best assets.
Butler is an excellent player, but I'd try to focus the Bulls on a deal containing 2 of the 3 pieces and a Pick 1 of C's 1st/DAL 1st/Rozier/Hunter.
I'd be very reluctant to trade Smart in any deal though. He has an excellent shot at developing into an elite player in due time. He's already elite defensively, but he has to be given time to continue progressing offensively.
Can he become an elite offensive player? There's plenty of evidence to indicate that there's a good probability of that occurring (once he becomes confident enough in his handle to drive on closeouts (ala Crowder), maneuver in the P&R, gets the benefit of the doubt on fouls, and reasonably improves in shooting accuracy, his scoring averages will jump).
The question then becomes... Butler is an All Star caliber player now, is he worth gambling on Smart and his potential to get to Butler's level, Crowder's continuous improvement, and the choice of one of the top collegiate players this year. He is, but I would gamble on Smart/Crowder/BKN 16 and not trade for Butler unless I could entice them with the deal mentioned above.
Would the salaries not matching up be a deterrent to this deal?