Welcome and how exciting!! FQ is lovely - we'll be there in Augsut too
At check-in you will be given a resort ID that you can put in the window on the dashboard. Each time you come and go from FQ you will use your key card to get thru security. It will also allow free parking at all the parks - and other resorts.
You can visit other resorts, but not park there for the day - i.e. to visit a park from the resort. But you can have dinner or visit the resort.
You might want to try Disney's transportation system - it makes you feel you are really immersed in the magic! Some do not like the buses, but at least give it a try - especially going to the MK.
MK parking is on the other side of Lagoon, so you'd have to take the ferry or monorail with day visitors...or walk over the the Polynesian and take the monorail to MK from there...much easier to just hop a bus at FQ and be dropped at MK
One thing we enjoy , esp in the heat of the summer, is to leave MK, hop the monorail and visit the monorial resorts (even if we are staying in one we enjoy spending time at the others). You can take the monorial to each one and spend time wandering around, enjoying the ambiance, having lunch etc.
Don't overdo it in that August heat!

Take a break and get cooled down, then go back later. It will make such a difference.
Have a wonderfully magical visit!!!