I’d certainly recommend a visit to HPWW if you’ve never been; I went for myself during the 2019 event (well, January 2020, but it was still technically the 2019 event), and I had a great evening!
In terms of hotels; I don’t know where abouts you live, but based on my experience, you could get some night riding in without necessarily needing a hotel. When I went, we only spent around 3 hours there, arriving at about 2:30pm and leaving at about 5:30pm, and my photo library from the evening suggests that it was pretty dark by about 4-4:30pm on the day I went (2nd January 2020); I certainly took a fair few of my rides at either sunset or nighttime! If you were looking at hotels, though, we stayed in the Premier Inn Kensington Earls Court hotel, and I will just warn you that that one is not as close as you’d expect; from memory, I’d say the walk was close to an hour, possibly 45 minutes at a push. According to Google Maps, Premier Inn London Victoria is a fair bit closer, at roughly a 27 minute walk away.
In terms of my ride count in the 3 hours; I did Olympia twice, the 4 other coasters once, and I also did HangOver, the big drop tower, once. If you were looking to cost save, it might be worth me telling you that in the year I went, 2 of the 5 coasters were bog standard Reverchon spinning mouse coasters (Ice Mountain and Christmas Coaster). Unless you’re into credit counting like I am (a non-kiddie +1 was never something I was going to pass up on, even though it was the same ride type as I’d just ridden!), or you really like Reverchon spinning mice, then maybe you could get away with only riding one of the two? (I’d personally recommend Ice Mountain if you’re picking between the two, as it has some rather nice theming and lighting for a travelling coaster!)
I’d really recommend HangOver, the drop tower, if you’re even remotely into drop towers. It’s absolutely fantastic, with great forces on the drop; it was by far my favourite ride at HPWW, personally, and certainly worth the money!
All I can really say other than that is that I hope you have a really nice time if you do go! I’d say it’s worth visiting at least once, if only to ride Olympia (and HangOver, if you’re into drop towers), and I did have a nice evening there!