Some people say its about an hour from GKTW to the parks, but we were just there a few weeks ago, and it did not seem to be that long. Having said that, I would still leave GKTW an hour before your reservation time, just becuase you are supposed to check in for your reservation 15 minutes early anyways.
Its fine to eat somewhere other than your park of the day. We had breakfast at Chef Mickey and then went to MK no problem. It will not eat up too much of your time.
Don't take the busses around. Drive yourself. My extended family was down there with us, but they stayed on the property and took the busses around. It took them so much longer to get around than it took us. You get a free parking pass, so you don't have to worry about that, and they will let you park in handicap, so you won't be in
"the back 40"
Don't even worry about which days are better than others to be at the parks. Just plan what works best for you. With the GKTW button and GAC, you don't have to wait in a single line, so it does not matter. Since you will have your own transportation, you don't have to worry about the busses being crowded and since you can park in handicap, you don't have to worry about that either. Really, its like being in your own little world without hassle

I had heard horror storys about the crowds at the wizzarding world of harry potter. It was crowded with lines, but again, we were able to bypass those and get right in and see what we wanted to see and get right out.