We are going just for the day on 12/10 to finish up a week in Orlando. We mostly want to see the Harry Potter stuff and don't care much about riding coasters. We will be taking our son who is 17 months. Is it doable to get the park to park pass and see most of not all of the Harry Potter stuff? As far as non coaster rides, would the baby be allowed on anything? The train ride maybe? Where should we start when we get to the park? We will be staying at a Disney resort but we will have our own transportation to Universal and plan on being their early in the morning.
Yes, you can see all of both HP sections in one day, even if it is busy. The baby will be allowed on the train, in the Ollivander wand shop for the wand choosing ceremony, can watch any stage shows, can go to any meet-n-greets, and can go through the tour only portion of FJ. For everything else, you will need to either use single rider line or child swap.
I'd start in US and head all the way back to Diagon Alley first. Ride Gringotts either single rider (since you will have to ride alone anyway) or use child swap if you can get there early enough that the standby line isn't crazy.
Some other things you may want to do in DA is to go in the robe shop and try on outfits for fun picture ops, check out Knocturn Alley, visit the sweet shop, visit the animal shop, and get a wand so you can do spells. Also, be careful of the dragon who shoots real fire; don't want to scare the little one.
Then, I'd take the train over to IOA and do Hogsmeade. You can all do the tour only option of the castle as a family without even needing a locker or anything. Then you can do single rider or child swap for the FJ ride depending on crowd. You can send mail by owl post if you bring a letter and stamp at the owlery. You can then have lunch in the 3 Broomsticks.
There are also stage shows in both parks you may want to see.
If you have time left over, I'd check out the play areas in both parks for toddlers. They are really cute and very nice. One of them has a neat ball pit.
Do you see the crazy wait times at Universal that you do at WDW?
I can't seem to find a list of rides that the express pass is good for, it's very expensive and I'm guessing we all need to purchase it for our ticket.
Yes and no. You do see long wait times when the crowds are at their worst. These can range from 30minutes to 2 hrs or more depending on the popularity of the ride. Most popular rides fall in the 1.5 hr to 2 hr range. Gringotts can be higher. You don't see the ridiculous 3, 4, 5, 6 hr waits Disney can have, like when people were camping out at Disney to meet Anna and Elsa or when Seven Drawrfs first opened. Also, mornings seem much better at Universal than at Disney. Crowds feel much lighter for popular rides. I've been able to ride a number of popular rides with no to minimal waits early morning at universal even during the busiest times when these same rides had long lines by lunch. At Disney, those long lines seem to build much faster within a few minutes of park opening.
If you are interested do a google search for universal crowd calendar. There's a really good free one out there that gives you estimated wait times per ride for any day of the year. It rates every day by one of 4 crowd levels, and then links to a chart that lists each attraction with the wait time listed for each crowd level. They won't let me post the link here, sorry. It isn't put out by UT or TP. I'm not sure how theirs compare.