your plan should be fine. regarding dtv try to get it earlier, they might tighten up the requirements if you are going the soft power route. you could fly to vietnam instead and apply, should only take a week to get approved.
if you are renting it for longer, try outside of pattaya. im renting a Mitsubishi mirage right now for 14 days at 600 baht a day in si racha, around 30 minutes from pattaya. they might be able to deliver as well
i did the wall gym in Chiang mai, but there are many others so over Thailand, they just need to issue an invitation letter stating your schedule and their business registration.