Welcome, and good for you for wanting to rescue a pit/amstaff!!!
Unfortunately, you will need to see what restrictions, if any, are in place where you will buy a home. There are breed specific laws, in many parts of the USA, which ban pitbulls.
You will also want to check with insurance companies (and lenders) about their restrictions. Here in Seattle, WA, I talked to my insurance agent about my pits (mixes!). She said that most insurers, including mine, restrict almost any big dog- but you are not required to notify them if you get a dog.
If you will be keeping your dogs outside for long periods of time, you will need to ensure that they are secure. This will not just prevent them from escaping, but also prevent anyone from getting to them.
has some good designs for outdoor kennels as I recall.
Different rescue groups will have different policies and requirements- some will want to at least know that you've talked to a vet. If you have a positive history with a vet, I would guess that is what they are looking for. Some microchip, some don't. MOST rescues that I've talked to will spay/neuter, microchip, and get the dog up-to-date on shots. They will pass this cost on to you as an adoption fee. If you work with a pitbull specific rescue group, you will have good odds that they will have done a good job of evaluating the dogs temperment- the "pound" may not have done this. One benefit of getting a dog, as opposed to a puppy, is that you will have a better idea of what the dog is like.
Do some digging through this site- especially in the rescue section, and you will find tons of useful information.
Good Luck, and post photos!!!