Just go with the Muay Thai classes, EVO360 gym in pattaya talk with Sharon - 6 months 20k Thai baht. Heard some horror stories on cooking classes and prices.
yes, so far everyone doing it only enrolls 6 months course and able to get the 5yr visa. Not sure if they will ask for extensions or northeastern in the future, but should be ok for 5yrs time at least. Lots of people doing it and successful, see DTV group of interested in entire process.
Your address from your home country is needed on the application. If your living in thailand and leaving to get this visa - so you will spend a few nights in cambodia or laos - you will also need your reservation of hotel. But your permanent address and the proof they need on bank statement or utility bills is for your primary residence in your country.