You'll need Metra Harness 72-5600. You can use any 5x7 speaker, it will mount fine. You can also use a 6x8" speaker as well, but you will need to slightly modify the mounting holes, and it will fit right in as well. You just won't use the end mounting tabs.
Running wires into the doors is an absolute nightmare. I suggest either taking the door right off, or paying someone to do that part of the install. The "molex" is a huge pita to get unfastened, and once you do get it undone and drill holes to feed the wires through, (plenty of room, just be careful not to drill into a wire) putting the rubber grommet back onto the molex is equally a nightmare. Then you have to contort and feed the wires up into the subframe of the chassis because the hole where the wires come through is hard to access. But it can be done. You'll need a lot of patience and either no kids around or a quiet voice. Swearing WILL help... Good luck
2011 GT C/S, MT82 Race red with all black interior
Conti Extreme Contact DWS's 245/45 ZR 19
GT500 axle-backs with resonator deletes, FRPP tune
BMR poly LCA's