If you are going to do this, I would recommend resort-hopping and spending 1-2 nights at Universal. The deluxe hotels there are similar in price to BC/YC, and just as nice in terms of overall theming/luxury. They are just as close to the parks and Citywalk as BC/YC are to Epcot/DHS/Boardwalk. Just like at Disney, you can get decent
AAA discounts. Obviously the pool areas don't compare to SAB, but the hotel pools are nicer than the Boardwalk pool area. If you stay onsite, you have Universal Express pass, which is like unlimited FP for almost all of the rides in both parks, all the time. It is so wonderful, you will be amazed!
The Harry Potter area of IOA is always packed, and will be even more so as Diagon Alley opens this summer. You will definitely want to see these areas over 2-3 days. Take advantage of onsite early entry and get into the Harry Potter areas before the massive crowds. Then take advantage of late morning/afternoons to see the other areas of the parks (or return to your hotel for a swim) before going back at night when the parks start to empty out. The HP areas are gorgeous at night and take on an entirely different character. You don't want to miss that!
For passes, take a look at the Universal section of this board. There is a good 'ticket discounts' thread.
So in short, I would recommend tacking on a couple of Universal days at the start or end of your WDW stay. This will help with cost and logistics, and help you get the most out of Universal! We do this every trip, including in a couple of weeks when we come to Orlando! We'll be spending June 21-23 at Universal, then transferring over to YC on the afternoon of June 23.