Need to choose first full IM

Italy sound nice. Can drink some good wine. Maybe between now and then you'll connect to some people doing the race so you won't be "alone". And wine. If I had the $$$ I'd go to Italy for sure. And wine. Food will probably be good too to go with the wine of course.

Haven't done full IM or a tri in Europe so not sure I can speak to course issues, but train travel is super-convenient in Europe (but maybe you're European so you know this!), so airport distance shouldn't be a serious issue. Most airports have an attached train station where you can get onto the rail network quickly. There are even special cars for bikes, and on many trains you could sit and "babysit" the bike the whole way. Or just rent a car. Medical checkup is probably just a formality--that was required in China, too. Though I know it can be a big expense if not coming from somewhere with socialized medicine (or not having a doctor friend who can take care of the paperwork for you). First-year event is always a bit of a risk, but IM events tend to be solid on the basics like safety and aid stations. I'd only have concerns (some, not overwhelming) in a developing country. But IM Vietnam 70.3 was okay--if they can manage that, they can manage Italy!

Course-wise, Italy sounds nicer. But only you know your comfort level with ocean swimming. I understand it is a different feel from lakes/pools and hard to really prepare for if you live far from the ocean.

Agree about food and weather. I've been to Amsterdam maybe six times for usually 2-3 days each (passing through en route to visit relatives or travel elsewhere, plus one week of bike touring in the area), and I can recall only 2 or 3 really nice days mid-summer. The rest were uniformly cold, rainy, and blustery. Personally, I'd go for Italy in a heartbeat! I think September you will have more risk of blustery weather. Italy should be nice--maybe a little hot depending on what you're used to.

I agree with Reece