Seconding the 'rent a car' opinion. You really don't want to be sitting waiting for Disney transportation to and from your resort. It works for some people, but I'd rather be on my own timetable. Plus, if you want to leave property for whatever reason (say, to go to Islands of Adventure, or Target because you want to keep some bottles of water in your room and don't want to spend 3.50 a bottle) you can.
However, since you specifically mentioned spring break, you may be under 25. In which case, you may not be able to rent. If that's the case, just make sure you give yourselves extra time so you don't run the risk of missing the bus and waiting another 20 mins, then missing your reservation.
I also recommend Port Orleans French Quarter. It's a moderate, a price grade higher than a value like Pop Cen or the All Stars. In my experience so far the values (especially during spring break time) will be very loud, and very full. Kids, teens, loud annoying people from all corners of the Earth flock to the values. POFQ, though - It's a small resort, quiet, very pretty.
Unlike Jme, I am a fan of the deluxe dining plan. It works out being more expensive per day, and yes it's a lot of food, but my wife and I worked it so we eat a breakfast or early lunch, run around the parks all day, then a signature dining dinner (requires 2 table service credits). It makes it feel so much more like a vacation if you sit down to a fancy dinner at night. You also get a bunch of snack credits that can be used during the day if you get peckish. Some signature restaurants are worth it, like California Grill, Jiko, and Narcoosee's.
This is all assuming you stay on property, if you don't, I have had very good experiences with the Hampton Inn on Palm Parkway, just north of Downtown Disney. I have never taken their bus service to/from the parks, but it's close enough to Downtown where if you do have a car, you can park in the Downtown parking lot (free) and take Disney Transport to the parks if you don't want to take their transport or pay every day for parking (IIRC, there are no direct busses from Downtown to the parks, you may have to take one to a resort, then change busses - I may have that reversed though).
Protip, skip the park hopper ticket option when buying tickets. You will not park hop enough to get value from it. Instead, buy tickets for a few days more than you will be staying. In Disney terms, a "day's" admission is just a single park admission. So if you stay for 5 days, buy a 7 day ticket, two of those 5 days you can park hop. Also, if you don't foresee yourself going to water parks, also take off the 'Water Park and More" option to save more.
I have also been to IoA many times, but only once while they have had HP. It was insane. We never even got to get into Olllivander's or Dervish and Banges. I don't know, but I assume it may have calmed down since Oct of last year.
Protips for HP:
-Get in the queue for Dueling Dragons (Dragon's Challenge) to watch the GoF themed Durmstrang/Beaubatons show. If you're not on the ground waiting you may not even be able to see it. In the queue there is an overlook where you can see/hear it perfectly, and no one will bother you.
- A note about this, the foliage may have grown in so you can no longer see the show. YMMV.
-If you want to see the shops, go ahead and wait to get in if there are lines. Otherwise, the main gift shop by the entrance to the park has 80% of the merchandise (including wands) and no lines.
-Don't get caught at the entrance to Forbidden Journey in something that looks like a line - it's a line for lockers, not because of lack of lockers, but because its a major bottleneck. They are strict about no loose articles on their rides. The tip here is to go through the gift shop - there's a direct entrance to the lockers then right into the ride queue.
But basically, have fun. It really is a wonderful place if you aren't cynical and can deal with people. Don't get heated about lines - enjoy the scenery, look for hidden mickey's, shoot he shit with cast members - they don't get paid much, most of them are there because they want to be. You may make their day as most people treat them like part of the scenery. And they may surprise you. We got free popcorn once, in a souvineer bucket because it was our Honeymoon. Another time we got like 6 anytime fastpasses for Expedition Everest because I was having a lively discussion about Yeti's with the CM at the entrance. Also, if its your first visit, anniversary, birthday, whatever, ask for buttons commerating the occasion. And wear them!