Get a Tecnics wiring adapter - makes the whole deal plug & play, with no cutting required. Also makes it a snap to go back to stock when your love affair with this car is over...
After that, it's all a no-brainer. There are several good writeups for replacing the door speakers & underseats.
Also, you'll probably want to consider moving the stock radio to the trunk - so that you maintain the chimes, and so that the dealership can check/update software. There are several threads here outlining this as well.
With a good adapter/harness, the total install should be about 5-6 hours (assuming that you've done this type of work before). The first door/underseat will take 2-3 times longer than the other side, so don't get discouraged if it seems to be dragging. Once you figure out exactly how to remove the door cards without damage, they pop right off.
I do recommend to get some of the plastic interior trim removal tools from Harbor Freight/Pep Boys/etc. They make removal of the doors & trunk trim safer and mark-free.