I use poplar for painted face frames. It takes paint very nicely and is harder than softwoods such as pine, so not damaged as easily.
Regarding pocket screws, if not using them what sort of joinery did you have in mind?
For the boxes, traditional methods would be nails or rabbets and dados fastened with nails. I prefer Festool dominos, but the tool may be too pricey for an amateur or a one-off project. The main issue I have with pocket screws in this application is that you have to be careful to clamp the parts so that they can’t move while you drive the screws else the screws may pull things slightly away from alignment. With a proper jig, boring the holes is reasonably quick.
For face frames, the traditional joinery would be mortise and tenon or perhaps dowels. Again, the Festool domino is essentially a loose tenon and serves well in this location. Pocket screws also work, again if you are careful to prevent the parts from moving while you drive the screws.
For fastening the face frames to the cabinets, the most common choice is nails, often with glue as well.