If you're staying onsite at Portofino Bay Hotel, Hard Rock Hotel, or Royal Pacific Resort, you get the unlimited express pass *no matter how you got your tickets*. It's a part of staying at the resort (no matter how you book the resort). Of course you have to have admission, but once that's worked out, the EP isn't connected ot how you booked/purchased anything else.
You literally take your room keycard, go to a kiosk in the lobby of your hotel, have a picture taken (you take the picture), and the unlimited EP pops out.
In terms of Wizarding World, you can use your EP on the two proper coasters; Flight of the Hippogriff (a bit of a "baby" coaster, but very fun) and Dragon Challenge.
All 3 of those hotels also give you Early Entrance to one or both (depends on the day) of the Wizarding Worlds in the parks. This allows you to more-easily get on the other attractions in Hogsmeade (the one in Islands of Adventure park) and Diagon Alley (the one in Universal Studios park) that aren't part of EP.
If you want to ride the train that goes between the parks, the Hogwarts Express, you *have to* buy a park-to-park ticket (a "hopper", in WDW terms). And the ride is different each way.
I book room-only through this site:
https://uo.loewshotels.com/en/booking/uo?hotel=UEPBH,UEHRH,UERPR
I buy my tickets from UO's site, from undercovertourist, from maple leaf tickets...wherever works. Actually, we bought tickets from maple leaf once, UCT another time, and I upgraded the two UCT tickets to APs (and bought my own AP on that trip direct from UO), and we've kept the APs since then.
You get the unlimited EP and the early entrance (for the 3 deluxe hotels) from the moment you check in (allowed at 6am, but if you're coming from a cruise you won't get there in time for that checkin day's early entrance) until park closing time the day you check out. Same deal for the other 2 hotels, for early entrance.