I swear Oda must be saving Cross Guild for a movie or some shit at this point
Mihawk to Green Bull.
Croc, Mr. 1, and Buggy to Impel Down for Doffy.
Green Bull is a loner swordsman who likes booze and took on a bunch of swordsmen/Samurai while calling them weak in his introduction.
Adding the Doflamingo Pirates to Cross Guild makes them a legitimate Yonkou-level crew in the race for the One Piece:
Yonkou = Mihawk (and Buggy LOL)
Commanders = Crocodile, Doflamingo, Daz Bones, (Bon Kurei if he joins CG)
Tobi Roppo level = Pica, Diamante, Trebol, Sugar, Senor Pink, etc.
Buggy, Doflamingo, and Crocodile have so many criminal/underworld connections that if they united, they'd be in a fantastic place to rule the underworld entirely.
Watch out for Neo Mads working to supply Cross Guild with weapons, too, since Wano, Dressrosa, and Buggy's weapon shipments are all dead in the water. Cross Guild needs a weapon supplier, and Neo Mads is the most likely group, IMO.