Cheers guys, useful stuff.
Unfortunately, as I say, I think we will have no choice about the dates - last two weeks in August I think. Nice to hear that it's doable, if uncomfortable.
This post looks like it's immensely helpful - except that I barely understand most of it, due to my lack of knowledge!
So the fast pass system isn't a 'pay to ride quicker' like it is at most UK parks? It's something everyone can do to some extent?
Correct for the Disney Parks. Unless the system has radically changed in the last two years, and it might have, anyone who buys any sort of multi day ticket (ie. everyone) can book fast passes one month in advance of their visit days so long as they have bought the tickets and registered them with Disney. On that day, all fast passes for the most popular rides ‘sell out’ in minutes. You can book up to three per person.
If you do this, you’ll find that many fast passes aren’t available at all. That’s because people staying on site in Disney hotels have a much longer period to book the tickets, so the same days are available say 2 months in advance. Also, the booking become available for the whole of your stay at Disney, 2 months in advance, so if your staying there for 2 weeks you can book some rides 2 months and 2 weeks in advance. Even with my tricks, I was unable to book passes for the most popular rides (although some of that was strategy, more on that later).
The second strategy I alluded to was the rebooking trick, which exploits that only one fast pass slot can be booked in an hour period.
So you could book 9am, 10am, 11am. Once you ‘check in’ for the 9am, you can immediately go into the app and look to get another one (in this example from 12am).
It’s actually far, far better to go with say 9am, 11:30 and 2pm, once you use your 9am, you can then rebook a pass for any time up to 10:30 (I.e. an hour before the next pass). So you theoretically get in multiple fast passes in your first hour of the park. Also, if you spread them out, you can always swap your later fast passes for earlier ones. There is an enormous amount of strategy with this. As a super bonus, I discovered that if I entered a Disney park on my regular ticket and then also synced my Halloween ticket up and scanned that at the park, I had two lots of three available! So I ended up stacking IIRC seven dwarfs mine train, Peter Pan, space mountain, pirates of the Caribbean and Jungle cruise all within 3 hours (there is probably one person reading this going “noooooo waaaaaaayyyyyy” - if you’re familiar with the system it was a very impressive achievement with those rides

)
But, there is also merit in going against your instincts. If there is one ride that had a 2 hour queue, and several rides that have 40 minute queues, it is actually more time efficient to use the above tricks the smash out ALL of the ‘40 minute queue’ rides without any wait and then just suck up the one big queue. Counterintuitive, but it works
There’s a great website called Touring Plans that has a set of ride calculators and calendars to help you be crazy efficient - it is worth the subscription and having a read of the forums.
As for the universal parks, it’s a more relaxed affair - anyone can buy the fast pass tickets and that’s that. I think it is absolutely worth spending one or two nights in one of their on-site hotels as you then get their fast passes for free, which almost offsets the costs. Of all of the on-site hotels there, I think the Lowes Pacific resort is the best and I would consider a two night stay there on top of your Villa stay if going to universal studios is appealing. The downside to staying on-site at universal is that food and drink, unless you are deliberately going cheap options, is expensive.... if fact it encourages you to be cheaper. But really, you’re on holiday and I think the convenience factor of staying at say Lowes Pacific massively outweighs the faff of driving, parking and having to pay money for fast passes anyway.
Oh and Typhoon Lagoon and Volcano Bay are both worth doing, the former for the epic wave pool and the latter for the excellent slides and ‘fearsome Lazy river’ which was absurdly fun
Again if you’re a coaster man (and I am a serious enthusiast) you really should make your way to Busch Gardens, especially with Iron Gwazi opening up. I was actually planning to fly to Florida just to go on it, so there is a lot of hype
edit - that first drop is 2 degrees steeper then Oblivion at Alton Towers, and it’s a taller drop, just to give you an idea of the epic ness.... no shoulder restraints either.