perhaps look into applying for the Covid extension of stay (currently able to apply until July 25 I think). If will either be approved or denied - in which case a notice to leave of 7 days is given. As
I think the legal implications would still be the same, whether or not the last day of stay is a Sunday. OP is permitted (I believe) to cancel work permit in advance (not sure how many days). Even if they go in ahead of time, the date of cancellation will be marked as the last day of extension of stay, not the day OP goes in. Best to cancel everything legally if there is a chance of returning at some point in the future.
OP already has visa issued. No need to visit country in any country - I would imagine entering country X is sufficient, then turning around and coming straight back to Thailand with the already-approved visa.
and that would mean starting monthly 65k transfers at the same time as applying for the first 1year, in order for the 12mth transfer method to be used NEXT year
There is technically no limit as to how many times you can get the 30+30 in a 12 month period, but the more times you do so will increase the likelihood of awkward questions at inbound Immigration control.