Welcome to a wide world of info.
I think the big thing will be the time that has gone by. Unless it is a really great dealership, I have an idea they are going to throw it back to you.
With that being said, I grew up on a rotary. So when I was ready to move into a DA quite a few years later, I had it narrowed down to a Porter Cable and a Gen 2 Griots polisher. I went with the Griots and love it. But you can't go wrong with either one. The Porter Cable has been around a lot longer. I think a lot of companies first DA polishers were just rebranded Porter Cables. But Griots machines are very well built also. And they have just recently re-did their 3" and 6" models. So they have improved on their older models.
More importantly watch some of Mike's videos that are related to the subject. Or some others that can be found on youtube. But, try and make sure that it is someone that has done it for a while. There are way to many people that need to quit making videos for youtube, and not just about detailing.