Keep in mind two things, you cannot apply for a DTV whilst in Thailand, and secondly no landlord will accept a conditional lease agreement. At best you can rent an apartment and pay the 2 months + 1 month upfront and simply forfeit if you don't go ahead
I'm also DTV holder but maintain an apartment in Bangkok. I travel extensively but for immigration purposes I have been at the same address for seven years. In your case yes, you'd have to do it on a case by case situation
days prior to due date via EMS so it's postmarked the date and is tracked. Immigration cannot claim they didn't receive it. I've used this process for years, hasn't failed once. I won't even try the online system. No point. It would save me at most 15 minutes and 70 baht, and with the thought that it might get rejected
Every time. I'm certainly not going to waste almost a day travelling right across Bangkok for a 90-day report. The post office is two minutes walk and has a photocopy service. I use EMS and the letter is tracked, so I know it reaches immigration.
I do every 90-day report by mail, I've never once reported in person. Mail works fine. I can't even be bothered using the online system, because if it fails, it's too late to do it by mail. The mail system never fails. Costs about 70 baht and about minutes at your local post office