If they’re doing the Technodrome as the vehicle for the third set, it would make sense to tie Krang to it. So my guess for box set 2 would be the Party Wagon (van) with Raph, Casey, Splinter, Baxter (sharing Mousers as an accessory) and a Foot Soldier. Box set 3 in the Technodrome would be Leo, Mikey, Rocksteady, Krang, and a Foot Soldier.
I’d love a slightly different lineup with Slash replacing Baxter, but the Mousers were a big storyline and it just makes sense to keep Stockman connected to Splinter…