Visa is valid from day approved. You get 180 days on entry then you either leave or extend ONCE for a further 180 days after which you MUST EXIT Thailand and re enter. Each entry can be extended only once. The last date you can enter Thailand is the valid until date shown on your visa.
Print the pdf of the visa , there will be no visa sticker placed in your passport. For bank account it will be very difficult as DTV is just a glorified tourist visa.
Brokerage won’t, it will be up to the country you apply in as to what they will accept . Some want 6 months with a minimum balance of 500k equivalent baht.
In which case you wont be getting a DTV visa as ALL income must be from online working online and you CANNOT have any income from within Thailand or have Thai customers.
Can’t see a gym membership working. You will need to have approved training with the length of course stated by the gym and which days you will attend. This will need to be invoiced and paid up front