Apologies if I provided only half the story (e.g. about accommodation), I was primarily commenting on turnaround time but added a few details that might have been helpful to others... I’ve uploaded the items you mentioned for previous visa applications but process / website has changed and weren’t required this time. Think the declaration has been built into the software now so you agree on-screen before submitting rather than print, sign, scan, attach a separate document.
Can’t comment on what would be acceptable instead of a letter from employer such as payslips from other poster. Think they’re looking for something to show you won’t work while you’re in Thailand so job / business / school to go back to or retirement income so don’t need to. Payslips probably wouldn’t cover it as you could have left that job permanently. This is only speculation on my part though, I’m not any kind of expert and only sharing my experience.