Hi Plain 1,
Welcome!
Firstly, 3 golden rules
1. Never pay up-front for flying training
2. Never pay up-front for flying training
3. Never pay up-front for flying training
Now, the straight choice between Biggin and Redhill. As you say, Biggin benefits from a hard runway, Redhill is grass (mostly!) I'm not sure what's happening about the taxiway, had heard the widening was in dispute. No matter, the issue with the grass at Redhill is mostly about waterlogging in the Winter. You say you're planning on starting in April, when the grass should be OK. As you say, Biggin is really busy with exec. jets. Whilst the big airports like Gatwick are like ghost towns, private jets are still operating so I would imagine Biggin will still be subject to delays.
Stick over yoke? I learned on a stick aircraft, then flew with a yoke, still sometimes fly with a stick. It's good to do both, can't say which is better to start with.
How many hours? Minimum for a PPL is 45, budget for 60. I was 33 when I learned, took me 58. The extra hours are never wasted (well, shouldn't be anyway) Make sure you get something out of every flight.
Book at least one flight a week, 2 if you can. 50% will get cancelled by weather. It'll still take you a year, unless you can invest mid-week time and make 4 bookings a week.
There are 2 popular sets of manuals, AFE and Pooley's. If you want to do some reading ahead of time, buy book one, either one will do. This describes the flying exercises in accordance with the syllabus. If you can find out which syllabus each school uses, then you can get that book. I wouldn't buy any of the other text books just yet, until you've discussed it with your instructor.
If you can, book a taster flight with both locations, so you can see for yourself not only how the airfield operates, but whether or not you're going to get on with the people, especially the instructors.
If I can express a personal opinion, I've done quite a bit of flying from both places (though not recently) and I'd come down on the side of Redhill and Cubair. However, as I said, you REALLY need to meet the folk at each place and see if you'll get on with them.
Good luck and let us know through these pages how you get on.
TOO