Re: buses vs. driving, my preference has always been to take Disney transportation even though it can often be slower than driving yourself--I like not having to worry about remembering where the car is and I think it's much safer not to have to drive when I'm tired from a long day at the parks and/or a little tipsy from a visit to one of the bars. And, too, I think they've started charging for parking at the resorts--someone correct me if I'm wrong?
If you've already done this please ignore me, but have you signed up for a My Disney Experience account, and have you already made any of your reservations? Everything you reserve through Disney can be linked to that one account, which also links to your MagicBands. That's where you'll make FastPass reservations, as well as any dining reservations. You'll want to link both your room reservation (if you're staying onsite) as well as your park tickets to the account, and you can link your accounts together to show that you're in the same party and make it easier to make joint reservations. You can access it through the My Disney Experience app if you have a smartphone, too, which makes it easier to adjust things on the fly once you're in the parks.
Also, regarding goals and whether it's too much to try to do almost everything in the four main parks, it really depends on how long you're staying. Are you looking for help with building an itinerary (how many days to spend in each park, etc.)? And have you decided whether you're doing one park per day or upgrading to park hoppers? Do you know what kind of schedule you'd like to keep in general--whether you're an open-to-close kind of person, or if you're looking to do things with a little more relaxation? Knowing a little more about whether you already have experience with WDW and how much planning you've already done will help us to better know what kind of advice to offer.