On question 2, my partner (a teacher employed by the government) has mentioned this to me as an incentive to get married. Not sure of the details or how true it is, but she seems convinced.
For the non o application, the money needs to be seasoned for 60 days. I guess it depends on the individual bank policies for how long they keep records. I have not tested that.
Come back on a visa exempt stamp. Then apply for a new non o at your local immigration office. That’s what I did in July. I was stuck in the UK and my retirement extension run out in February. No hassle at all.
The first time (in Korat 10 years ago) I needed a document from the bank showing evidence of a foreign transfer. I think that is still a requirement. I guess they didn’t ask for that in July because they had done my annual extension based on my deposit account a few times before, so although I was making a fresh application, they knew I had shown evidence in the past.