Hi Lister - I'm typing this after 5 pints of Abbots Ale so apologies for any skewed thoughts and typos.
1. Revalidation is evey 24 months from date of GFT with a minimum of 12 hours of P1 flying (inclusive of 1 hour revision flight with an instructor) over that 24 month period as long as 12 hours are flown in the last 12 months of the 24 month period. In other words, you can fly as many or as few hours as you like in the first 12 months of the 24 month period but they don't count towards your PPL revalidation - go figure!? Anybody crazy enough not to accrue flying hours in the first 12 months just shouldn't be flying!
2. Revalidation flight can be taken anywhere within 3 months of the PPL expiry date.
3. Need to complete 3 take offs and landings within any 90 day period to maintain currency to carry passengers.
I may be wrong and no doubt others will have a view on what's what, but hope this helps?