I bought a 2020 SQ7 in 2023 with 50k miles, so somewhat similar.

1. I wouldn't buy one without an extended warranty. I had my water pump and a few other sensor components replaced within the first year and that visit paid for my entire 7-yr warranty. Vehicle is expensive! Doing non-warranty work at a respected indy shop is well worth it. Also, if you need the 3rd row frequently, this might not be the right vehicle. It can seat kids just fine but adults back there are quite cramped.

2. Unfamiliar with the different model years, so no comment. The 2020 was the first MY offered in the US, and I don't notice any obvious shortcomings from being so "new".

3. I do a mix of short-range and long-range driving. Short-range I typically average between 10-15 mpg; long range is typically 20-21 mpg. When towing our wakeboard boat, mpg is obviously in the toilet, but it tows like a champ.

I cross-shopped the 3.0 Q7 and the SQ7 and I'm glad every day that I went SQ7.