-I would hit GK and (Wild Mouse if you are interested) and then camp at your favorite ride. Seems this will be a super easy way of getting on MIllennium and Maverick. I am willing to bet there will still be a solid contingent of people who go wait at SV right at 9am though.
-Last season the park got back to closing rides at park closing time. No more closing rides 30 minutes before closing if there is a 30 minute wait. However I would not expect them to keep lines open late like they used to in the past. Everything should close on at 10pm (or whatever time closing is) on the dot.
-Yep exactly that. I stayed there for my first time during opening weekend of haunt last year and didn't touch my car once. It was nice.
-I would avoid leaving the property. Perkins is reasonable if not the same price as their other locations. As others have said there is also a walk up counter for grab and go type stuff. There is also a starbucks inside of Breakers and one at the front of the park that I believe both serve all the typical Starbucks breakfast food.
-Fastlane is available at a number of giftshops in the park. The ones that come to mind are the main giftshop at the front of the park, "Point Plaza" and also the General Store that you pass approaching Maverick. I believe you can also redeem at all ticket booths at any entrance to the park. There is also a fastlane specific walkup stand to the right immediately as you come through the main entrance.
-Lockers are easier than you've been led to believe. It really is a seemless process. Especially mid season when the ride ops have good control of the situation down there. But yes you'll wait in FL+ queue, drop stuff in lockers, go through metal detectors, wait about 10 minutes if not less, then get on the ride.
-I'm not sure about your monitor. You might be safer getting an ADA pass for this situation specifically. Go to Guest Services and explain your situation and they will take care of you accordingly. If I had to guess, they'll give you a pass in which a member of your group waits in the FL+ line and you wait near the ride exit. When the rest of your group makes it into the station, you go up the exit and you will drop your monitor in a ADA pass specific loose article bin, ride immediately with your group, then get your monitor back right away. If you are alone, they will give you a pass where you go to a ride, get immeidate boarding, and then are given a wait time in accordance with the ride you rode that will signify the next time you may ride a ride using the ADA pass. So for example, you go ride SV right at 10am and it has a 30 minute wait already. You will get on SV right at 10am with ADA pass, and then they will write on your pass 10:30am. So then at 10:30am you can go to any other ride at get immediate boarding and then get another wait time and the cycle continues. All in all, I seriously doubt they'll allow you to take your monitor on the ride, but the ADA pass will allow you to spend minimal time without it.
Hope all this helped!