Personally, I wouldn't waste a ticket on a half day at Universal. When the parks stay open "late", it's only until about 9 or 10. With Disney you can usually get in a good 8 to 12 hrs even arriving after lunch when the parks stay open late which for Disney is past midnight. However, in comparison Universal closes ridiculously early, 6 sometimes. Looks like 9 for both parks for your dates. That would give you maybe 6 hours if you arrived at the park by 3. Not a lot of time.
Instead, I'd take advantage of some other form of entertainment on arrival day, hang by the pool, play mini-golf in Citywalk (Uni's version of Disney Springs, only its in walking distance of the hotels and parks), catch a movie in Citywalk, go bowling at CB (onsite hotel), see the Blueman Group show in Citywalk, eat a fun themed dinner at Toothsome in Citywalk. I've had family members tell me the mini golf at Universal is some of the best themed they've played anywhere.
If you have a car, you can always catch some other attraction on the way down or nearby as well. The Showcase of Citris is a fun place to stop for an hour or so. There are also a number of dinner shows in Orlando.
As far as the number of days to go, I usually recommend 3 days for newbies if you want to see everything. This gives you 1 day per park and then an extra day to go back and catch anything you missed and to reride any favorites. If you are going only for HP, you can see both areas in one day easily.
Some things to note:
Park Hopping:
I don't hop much at Disney. It takes so long to get from one park to another that it isn't really worth it to me. However, at Universal, I find myself hopping back and forth between parks all day long. With the train going between parks at the back and only a quick 10 minute walk from one gate to the other at the front, it is very easy and convenient to switch parks at Universal. It is more like changing lands than changing parks. Sometimes a ride in the other park is actually closer to you than a ride in the park you are in. The ability to change gives us more options for meals, catching shows, riding headliners in both parks at off times, and adapting to bad weather that may force us onto only indoor rides. Also, you must have "hopping" privileges to ride the train. They will not let you use a second day's ticket to enter the other park by train. You must have a Park to Park ticket.
Room Occupancy:
Technically, you can put 5 in most rooms at the deluxe hotels. I wouldn't want to, unless one of them is a very small child. To me, the rooms feel crowded enough already with 4 people, but we are use to renting condos and houses when we travel. You can request the rollaway if you need it. Either way, you will need to make them aware that there is a 5th person in the room, so you can get the EP for that person.
Deluxe Hotels:
There are 3 deluxe hotels. These give you EP passes in addition to access to HP one hour early. All Universal hotels give you early entry, but only these 3 give the passes.
Royal Pacific
South Pacific theme (Fiji / Hawaii)
2nd closet walk to the parks about 10 minutes
Closest to Island of Adventure Park
Room size: 335 sq ft, smallest rooms
Usually the cheapest option of the 3 resorts
Portifino Bay
Italian theme, Cinque Terre inspired
Farthest of the deluxe hotels, about 15 to 20 minute walk
Closest to Universal Studios Park
Largest rooms at 450 sq ft, if I was adding a 5th person, it would be at this hotel where the rooms don't make me feel like I'm crammed into a sardine can
More expensive rack rate than RP, but sometimes there are discounted rooms for better rates than the discounted rooms at RP
Hard Rock
Rock and roll theme on inside, Spanish colonial on outside
Closest hotel to the parks, with reports of pool gate to park gate taking 4 minutes to walk
Closest to Universal Studios Park
Room size: 375 sq ft, slightly larger than RP
More expensive than RP, sometimes more than PB as well, I haven't seen as good of discounts here as with the other two hotels, but that may just be me not paying enough attention as the hotel theming doesn't appeal to me at all. We are staying here in a few weeks, and I'm trying to be happy about it, but after walking around the hotel a couple weeks ago, I'm not impressed.
Thrill Rides / Motion Sickness:
Even though Universal doesn't have a ton of coasters (only 3 outdoor, 1 indoor, and 2 kiddy), most of what it does have could be classified more as a thrill ride than anything else. I made the mistake of going with a friend recently who told me she doesn't do coasters. I said, "Ok, no big deal. There is plenty of other stuff for us to do instead." Well, what she actually meant was I don't do thrill rides. She wouldn't ride anything that was a coaster, went fast, was up high, spun in a circle, or caused motion sickness! This pretty much ruled out 75% of what Univesal has to offer. Please be aware of the types of rides Universal has, which rides can cause motion sickness (like half), which are intense, go fast, go high, are dark and scary for kids, have height requirements for kids, etc. This will help you in determining how much you actually want to do and how many days you need. You may also want to check with a Dr about motion sickness medication if you are prone to it. I don't need any medicine at Disney but a number of rides at Universal make me sick if I don't take something before riding them.
Water Rides:
Prepare to get very very wet and on the raft ride, possibly completely soaked. I mean jumped in the pool with my clothes on soaked.
Lockers / Lanyards
Unlike at Disney where you can take small bags on any ride and larger bags on most attractions, at Universal many of the rides require you to store your belongings in a locker before riding. The lockers are free to use. Some love them; some hate them. Personally, I find them a little annoying and inconvenient at times, but overall don't hate them and don't mind using them once or twice. The outdoor coasters are even stricter, requiring you to empty your pockets completely. Nothing can be taken at all on those rides, and they use metal detectors to enforce the rule. Because of this, many people carry lanyards or waist money belts instead of bags because those are the only things you are allowed to keep with you. The lanyards are great for EPs as well because they have a barcode on them that must be scanned at every ride to enter. You don't want to have to keep pulling that out each time you want to ride something.
