Get the Non Imm O visa in the Uk, £60 and then get the 1 year extention of stay at your local Immigration Office, 1900bt. You will need 800,000bt in a Thai bank account for the extention. Just seen you're not 50 yet so forget this post. Apologies!
You need to update your bankbook on the day you apply for your one year extention of stay in order to prove your 800k Baht has been in there for 2 months. The bankbook will update with all transactions on the day you update and apply for your extention.
Only #2 and #5 are correct on your list. There's NO jet lag between Thailand and the UK! Plenty of authentic Thai food, especially in London. You can easily install a 'bum gun' if needed. The clothes will go to good use in Thailand (it does actually get cold there)