You may want to look at something like the PPI 4125 (125x2, 500x1 @ 4ohms), or the MTX Th1004 (same)....or another enormous 4ch to put some power to the sub.
I used to run it like that and it worked fine. I would strongly recommend going that rout over using a 2 channel for your subs then a deck for your mids. I haven't had much luck powering mids with a deck.
In 96 Sonoma Extened Cab (my beater) I have a 4 CH. Hifonics amp to Power the Fronts/Rears and a second amp for the Sub....
Im my 2000 Blazer, I have a sepperate amps, one for fronts, one for rears and one for the Subs... If I ever get my wall in, I will use the rear amp for a second set of Comps in the Doors or Kicks...