I used one to come here in August- it worked a treat to satiate the Goons at Singapore Airlines check-in; Who just follow a script and ask for your return flight. In other words without that, I'd prolly still be back in Melbourne.
I did what you want to do from Australia and prepared everything for the 90 days. Including; Insurance, fake burner ticket home after 90 days, 76 days 'reserved' accommodation (not paid for)- after the 14 days Sandbox. You could go this route OR prep everything for just the 60 days and then extend in-country and change your flight (as Stuart mentioned).
Keep your eye on the covid extension and whether they will re-up this. Announcement coming in a week or so. If you receive covid ext (get it late Dec.) you will have almost 3.5 months to play with from today's date. From there you can get ED visa or go straight to work visa.
It's a passport sized photo, but everything can be obtained at their office for a small fee. A few pages of your passport will need to be photocopied but it's easy to just do it there. They supply all forms to fill out as well.
More than likely your going to CheangWattana Division 1 Building B. You can search this FB group for more info on BKK immigration. I went last week and got there at 9am and was out by 10am, with a further 2 months Covid ext. If you get there early the process is relatively simple.
I tend to think just bring cash and change it here at small booths to get best rate. I personally have never had a bad experience here or lost money so what's the point of getting a money card... If you 'take care' you don't really need those money cards. Rinse 2k in cash then use ATM if you run out.
I went 1 day before expiration (which gave me one extra day to work with if something went wrong). For me it was processed the same day so it was OK to go towards the end of my visa expiration.
The chart posted on this thread by Bobby Howard is your best source. When I flew to Chiang Mai a few weeks ago it was also difficult to find firm info on this. For the most part, if your vaxxed, your OK, I've taken 4 domestic flights since Sept and no test required. Some of the Airlines have charts like the one posted here- your best source.