Does the agent mean you need more money in your account in the UK? If so he’s probably right and not a scam like all the experts on here are telling you. To get the visa you need to show you can support her in the UK, so money needs to be in your account not her’s.

Wrong

If you have no visa it is very risky to fly on a one way ticket they will probably refuse you. There are websites that let you book tickets and then get a refund (less a small charge) for this very reason. Sorry I can’t remember the names, they basically rent you a ticket to get round your problem. Do a Google search. Otherwise yes book a ticket out of Thailand. On the few occasions I have travelled on a one way they have always asked for a booking out of Thailand.

You cant get a cert from NHS with your passport number on it. Just upload what you have you will be OK.

Battleface if you want full travel insurance when travelling against uk foreign office advice but not cheap.

Battleface will cover you,

Your COE is based on your flight and ASQ booking if you want to go on the 15th you need a flight booking and ASQ for that date then apply for COE. COE's are issued quickly after you apply,

in UK yes

I sent an email from from the other halfs' account to me, inviting me to stay, that was accepted

The process seems daunting but its not too bad, non o visa takes a few days COE took a few hours. Just have to stay covid free and your good to go.