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)
It can take at least 6 months after your child is born to obtain custody rights because you need to go through the Courts. Your best bet is using a 'border run' agency.