I would call my trip a success for the most part although there are a few things I wish I would of done instead. The most important thing is to not to underestimate the weather.
Bring a trench coat and rain boots not a leather jacket and umbrella to Europe
When I was packing in late August/ Early September Europe was going through a heat wave. According to weather reports there might be a few days that it might rain but I was worried that I’d be too hot in a trench coat. Also bringing even my ankle rain boots would take up more space in my suitcase. I opted for a light leather coat and an umbrella instead. This was a HUGE mistake! I was hot in Amsterdam and Prague but it rained in every city I went to. The worst of it was in Vienna, I couldn’t predict torrential rain and strong winds but it made my umbrella useless. I tried to make the best of it. It was a Sunday so as soon as I got in to Vienna I went to the closest kilo shop from my hotel and luckily found a trench coat. Although it was light and had 3/4 sleeves. I could of really used my longer, warmer trench coat in the cold biting rain. It wasn’t completely waterproof and neither was my belt bag or purse. It was a little stressful trying to keep postcards I bought dry before I could send them. I recently bought a waterproof belt bag from Vessi that I’m bring on my next trip.
I won’t make this mistake again. ALWAYS bring proper rain gear just in case.
IF activities or sites could be effected by weather buy tickets ONLY a few days in advance
I’m a planner, so much that I consider trip planning as much of a hobby as actual travel. So I’m prone to buying tickets in advance but I learned this isn’t always wise. I’ll still buy transportation and accommodations well in advance but I have hopefully learned my lesson about outdoor sites.
In Vienna I bought all my tickets for the palaces in advance but the Schönbrunn Palace has beautiful gardens that were getting flooded with all the rain. I switched which days I did what but that meant eating the the cost of the tickets I had already bought. I was somewhat lucky that my last full day in Vienna I had a walking tour scheduled and had time to go to the Palace after that. Although the Hunting Lodge, Orangery, and Maze were closed due to the rain. The Palace was stunning and the ballroom reminded me of Beauty & the Beast but the Maze was what I really wanted to see.

I could not have changed the weather but I could have saved money if I had waited until a few days before to buy tickets.
Buy an e-sim with a top-up package
It was my first time buying an e-sim but I had good things about Airlo. I thought that I would have enough and the package I though was best didn’t have a top-up option. It did last me most of the trip, I think if my eventful train ride to Budapest had WiFi the whole way like it was suppose to I might have made it through the trip with enough data. I was starting to run out in London. I had to buy a whole different e-sim because I didn’t have an option to top-up my data. It’s annoying because you have to uninstall the old e-sim and reinstall the new e-sim.
Next time I’ll buy an e-sim with the option to top-up even if the base package has less data.
Go to the bathroom after passport control and customs but before luggage claim
On my trip I went through passport control 4 times but only had a checked bag the last time. In Amsterdam I went to the bathroom first. I hate using the bathroom on planes and needed to activate my e-sim anyways. I’m not sure if I could of gotten through passport control faster if I had waited but It was the longest line on my trip. The machines gradually all stopped working so everyone went through 2-3 agents manually. It took around 2 hours. In DC I went through in 5 minutes because I have global entry but I waited for my bag before using the bathroom. This was a mistake because it at least felt like it took forever then, I had more bags I had to take in a bathroom stall with me because I was alone.
These aren’t major mistakes but I’ll have a smoother and more comfortable trip next time.