Does footprint matter when selecting a part in Kicad?
Yes, you can select specific footprint later. And you can choose any footprint you like. Footprints that are assigned to some component are just filters or hints. If some MOSFET component has only "SO-8" specified, you can bypass that and choose completely different footprint.  

In addition to that, DPAK and TO-252 is the same footprint. Sure there is TO-252 footprint in Kicad libraries.