Congrats on your win!
It sounds like you will have 2 full days at the park (one day for each park), which is enough time to see and do almost everything.
First off, great idea about staying onsite! If the cost of the room is a little much, you could stay onsite for one night. For example, lets say you want to go to the park on Sat. and Sun. If you check in bright and early on Sat. morning, you will have express access to nearly (i will get to this in a moment) ride at both parks. Then, Sunday morning check out bright and early and either leave your stuff at the hotel or pack it in your car. That check out day you will also have access to the express line. So, you get two full days of express access for the price of a one night hotel stay! Of course, if money is not an issue, I really suggest two nights simply because of how nice the hotels are and not having to worry about checking into an off site hotel after your full day of park visiting the 2nd day.
Now, for express, like I said you get it for nearly every ride. The main HP ride (FJ) does not have an express access line nor does the main roller coaster at the Studios (rip ride rockit). There is also a ride in the Jurrasic Park area, but I doubt you will be able to ride it anyway because of the odd height requirements (it requires a shorter person to ride with a taller person like a child and a parent...your not missing much anyway).
Now for the dining plan. It really depends on how much you can eat. A thing to keep in mind is the park hours will be short during Sept. and Oct. (with the Studios closing around 5 or 6 pm and IOA closing around 7). Food service STOPS roughly 30 minutes before the park closes (sometimes sooner). Also, you are limited to the places you can eat and they are all your standard counter service food like burgers, hot dogs, chicken nuggets, etc. If you can eat 3 meals each, then it is worth it. However, their are MUCH better food options at the 3 onsite hotels and Citywalk. I would suggest a small counter service meal in the parks, and then when they close (remember they have short hours) enjoy a nice sit down meal either at Citywalk or your hotel. Also, the Three Broomsticks at HP is NOT part of this meal deal!
Since you will be there for two days during a normally slow time of the year and you have express, you should be able to see and do almost everything the parks have to offer. Do HP first (and with a hotel stay you can get into the HP area 1 hour before the park opens!) when you go to IOA and then just work your way around the park. I would do HP, the Suess, Marvel, Toon, Jurrasic Park, and then end the evening with another stop at HP (because it looks so good at night!). For the Studios, you will want to do Rip Ride Rockit first thing because they do not have express and the line moves fairly slow on that ride. From there, just work your way around the park.
Another thing to keep in mind is the fact that Halloween Horror Nights (
HHN) will most likely be going on if you are going late Sept. and will for sure be going on during Oct. If you are a huge fan of haunted houses and stuff, HHN is really top notch. I personally have never been because I am too chicken, but from the photos and videos I watch from the comfort (and safety) of my own home, it looks amazing (and scary). This is a hard ticket event, meaning you have to pay extra to attend. However, the event gives you access to nearly all the rides and the roughly 8 haunted houses and whatever shows they have for this year.
If you decide to do HHN, I HIGHLY suggest doing IOA on the day you are NOT doing the studios. The reason for this is simple. If you do IOA the day you are doing HHN, you will want to leave IOA before it closes to see HHN since it takes place in the Studios. However, this is all based on the past. No information has come out this year about HHN and with the whole Jaws area now closed, they might go back to their old ways have putting HHN in parts of BOTH parks (in which case they will both close early). No matter what happens, I would do IOA on the day you are NOT doing HHN to get the most out of your IOA day. Also keep in mind that your express passes will NOT work during the HHN events. You can purchase a HHN express pass that will let you skip the haunted house lines along with the rides for the length of the event. More information will come out as the event gets closer.
As far as doing something else in the area, Citywalk is always free! So on your departing day you could play a round of mini golf on the brand new courses (they should be open by Sept. I would hope) or just shop around. However, I am a little confused about needing to do something on your arrival day. If you are arriving early, check in right away and hit the parks. If you are arriving late, you could stay on the onsite hotel and enjoy a nice meal at Citywalk or explore your hotel. Of course, doing this would then require you to stay an extra night.
If you have any more questions, feel free to ask them!