Hi! We are doing 1-2 days at Universal, then 1-2 days at Disney, so I am looking into all of these questions as well. The Universal Hotels have transportation to the Sanford airport, for our party of six it was expensive, like maybe $50 per person? Since we are getting a car after our Orlando time and driving to the beach, it turned out to be cheaper to get a rental car for the full week, even though we will barely be using it during our park days, once I added up transportation to/from airpport and in between Universal and Disney. So once you add up your transport costs, check rental pricing, you may be surprised!
Early entry is for both Universal Parks. Our favorite easy tip for Universal (and Disney) is that early morning and late evening are the best times at the parks. We've been to the Universal Wizarding World of HP at park opening, and after an hour it was too packed to move, but if you go back after dinner everyone is gone. As more of Disney regulars, we feel like the crowds are harder to manage at Universal, so we're trying Express Pass this time. Also, we've stayed at Royal Pacific (Universal) once, and found the breakfast not worth it...crowded, expensive, and mostly carbs. The hotel however was lovely and very close to the parks. You'll be so pleasantly surprised compared to Disney how fast you get around your hotel and to the park...on foot!
To the original poster...as I plan our combination trip, there is a lot to figure out, some of the things I am keeping in mind as I consider which hotel for which days are: Benefits of Royal Pacific (Express Pass, if you want it, but it makes your hotel room way more expensive than you can get at Universal's Cabana Bay). If you don't want Express Pass, Cabana Bay is quite a bit cheaper and reviews are good. Or if you want it, work out how many days you want Express Pass for...it could be cheaper to stay at Cabana Bay and purchase your Express Pass separately. In general I am finding the Disney Value resorts a bit cheaper than the Universal resorts, so that's something to think about for your transfer day...stay in the cheaper hotel! But, consider Extra Magic Hours too, if you want that benefit at Disney. I did find out that you get your Extra Magic Hours benefit and, at Universal, your Express Pass benefit, on both your check in and check out days. It's a LOT to figure out, I've been working on it for a week, but it will be worth it in the end; I like to make sure I have it all planned out the best, cheapest way. I would also say, with the early entry benefit at Universal (Cabana or Royal Pacific), it might make sense to stay there the night before you will be touring there...so you don't have to get up at 6am to get out of Disney and over to Universal by 8am, for example. Royal Pacific is an easy 10 minute walk to the park gate, Cabana Bay (I have heard) is about a 10-15 minute bus ride.
Park tickets for 1-2 days like this are expensive, and it doesn't seem like there is any getting around it. Which is why I want to maximize our in-park time by staying on site and using hotel benefits like early and late hours and Express Pass. That's what is making switching hotels worth it to me (and the time saver from the drive between parks).
Finally, I have learned that you can get an Alamo Car Rental from the Disney Car Car center (accessible via Disney shuttles), however it is surcharged, so again it was cheaper for us to rent from the airport for the full 9 days of our trip rather than try to rent from Disney and not use a rental car during the 3-day park portion of our trip.
