If your car is new, few weeks old, don't need to polish, imo. Also, when I tried decontamination on my Model Y, 3 weeks old from the factory, did not find anything to be removed, so you might not need this either. But definitely, you don't need to polish, don't waste your time on this with a new car. I used AvalonKing coating, it took me about 6hrs from start to finish (prep the car and coating the car). Also, I like to mention, any consumer coating will last you only 2 years max, whereas if you do professionally, it will last 5 years.
Yes, you save money. But if you can find a cheap professional, you might want to consider it. My co-worker had his car for $450, guaranty it will last 5 years, had I known someone did it for $450, I would not spend 6hrs to do it myself
The process is easy, it just takes a lot of time to do it. I would say anyone can do it if you have patience. Remember, the most important part it's buffing, you need to wait for 2 to 10 mins depending on your room tempature. If it's summer, usually 2 mins, then you need to wax if the towel. The best way it's to wait for ceramic the change it's color like the rainbow, then you need to wax/clean up with towel. I have weak eyes, so I did the timing.
Is worth it? Definitely big YES. Either you DYI or professionally is a must-have to me. Your car will shine, it will skid all water, also very easy to wash your car.
Every new car, all of them, have issues to correct when new. If you didn't find anything on your Model 3, you either weren't looking hard enough or don't know what you're looking for. I found TONS of issues on my Model 3, a March 2020 car. Most were no big deal. A few were bigger and I had them addressed when I had my PPF installed. And they aren't immediately apparent to like 90% of people. But when corrected, 100% of the people could tell the difference.
This is not a Tesla thing. In fact, Ferrari has some of the worst paint in the business from the factory!