The 400k in a Thai bank is required to extend an existing Visa while in Thailand. Last time I got a Visa in my country they required me to produce a bank statement with a minimum balance of 6000 Euro (single entry non O). The last time I applied for a Visa it was in Ho Chi Minh. I payed 200 USD and no fund proof required (multiple entry non O). All pre covid, things might have been changed meantime
You don't need to pay a visit to Embassy. Only those who don't have a license written in English do. Because they need to have an English translation out of their license and so they need a stamp on the translation by their embassies
can be done with UOB (at least Central Bangna branch). Passport and a rental contract are enough. The only drawback is that they require an initial 50k baht top up. In short, you go there with 50k in cash and 1 hour later you walk out with a brand new account having an initial balance of