It does sound silly but that is what others have done with rental businesses for the DTV. Take the path of least resistance and takes about 5 minutes to produce the letter.
Even on a WP with a good salary they are reluctant to give out Credit Cards - I mean salaries with 250k++ THB per month going into account they can hum and ahh over a CC. The might give you a card with a limt of what you will put in an escrow but it is same as Debit Card really what you get anyway.
How will they know? If you were to apply for an extension inside Thailand at an immigration office, you would need an updated employment letter from the company. However, if you do a border bounce, ie re-entry, they are not checking this level of detail.
It will highly likely be a random officer. There will only be something in the system if he wrote it. To me it looks like you will be fine is 1) You update the letter etc what says you can work remotely and 2) an up to date bank statement showing the 500k This is what others have had to show - have a search. You should be fine.
Anonymous participant 524 Residence Certificates are issued by immigration. Years ago some banks wanted a letter from an Embassy but many embassies will not issue anything. As far as I am aware they wanted a Residence Certificate from immigration ratified by an Embassy that it was you. That is the understanding I gleaned fron Bangkok Bank staff on Sukhumvit Bangkok. It was moot anyway.
Depends on the Immigration Office and their mood on the day. At Jomtien I returned from Vietnam and re-registered the TM30 myself. Next time a month or 2 later tried the same and was told no need go away. Since moving to Chiang Mai I have been told I need to do it even for domestic travel but agent will do it for me. In Bangkok on BOI visa for 4 years I never registered TM30 at any time. The only constant is inconsistency.