There are a million questions here but I’ll try my best.
First of all: when in May? Are we talking Memorial Day weekend here or mid-week in early May? There’s a massive difference.
As for the hotel question, it depends but if you’re not wanting to rent a car I’m tempted to tell you to stay on-site. First off, you’ll save on the hotel parking fee. Second of all, while some nearby hotels that I do like offer a shuttle (The Comfort Inn on Canada Avenue comes to mind), it’s easier to just use Universal transportation when leaving the parks.
Their budget hotels are very competitive and reasonable and you get in early. If you want to go bigger, stay at a hotel with free Express Pass. Some of those hotels (like Royal Pacific) are also just fantastic hotels.
The Universal AP is a great deal compared to their day ticket but price it out. Note that if you come back in the fall you can ride Mummy, so that alone may convince you. You know what days you want to go though. Put it in the calendar and price it out. There are really no additional considerations here so it’s 100% a matter of admission price. The Seasonal Pass has no benefit aside from admission whatsoever unless they run a passholder hotel deal which they usually do in September.
Two days is perfect. Express pass will probably make your day better but whether-or-not you “need” it depends on when you go. Memorial Day? Yes. A Tuesday and Wednesday in early May? Maybe not. It’s never a bad thing to have it, but I get that it can be incredibly expensive and it doesn’t work on Hagrid’s or Velocicoaster which is annoying.
If you want Express, look to stay at a hotel that includes it. It may be cheaper than actually buying it separately for two days and you’ll be at a better hotel where you can walk or take a boat to the parks.
If you’re there for two days, every dark ride and simulator is worth riding except for Fast and the Furious and Fallon. Minions is cute but tends to get insane lines for no reason so it’s skippable without Express if the line is long. If you get express, then just ride every ride except for Fast and the Furious because seriously f*ck that ride. It sucks and has two horrible pre shows that you’ll need to sit through too. The only reason to ride this ride is out of morbid curiosity or for bragging rights so that you can say you’ve now ridden the worst ride in Orlando and possibly the world.
The water rides are all good but note that while Jurassic Park River Adventure is a must-ride, the other two are much wetter and will positively soak you to the bone. Don’t ride Ripsaw Falls or the rapids if you’re not okay with that.
Don’t miss the Bourne Stuntacular.
Best food: Disney Springs
(uh… I mean… I don’t know, I liked Big Fire and Toothsome).
Just Uber to the park, it’s not that far.