We got a 60 day visa which we extended by another 30 days at immigration in Bangkok. Our original 60 day visa was issued at the Thai Embassy in Cambodia aswe were already in SEAsia. We had also looked into applying at the Thai Embassy in Australia but you had to enter Thailand within 90 days of the visa being issued and that didn't work for our trip.
We rented through hertz they have been good. We were able to pick up in Bangkok and drop off in chiang mai with no additional cost. They also have no excess insurance. We checked the price with a few local companies as well and found hertz price was similar.
This was the advice I was given and it was extremely helpful. Do not go without an appointment unless you want to wait for hours. I followed the advice given and was done in less than 1 hour.