Let me start by saying this was my first major and my first marathon so nothing would beat the feeling of accomplishment I had finishing it.
We went to the expo by metro, it was easy to walk there following the runners. Expo was huge but bib pick up was easy and really fast. However, the lines to pick up preordered items were terrible and unorganized, I think I was there at least for an hour waiting and it made me want to go away right after I picked up my stuff. I went to the shop near the zoo which was ok to buy race merch the day after the race.
We stayed near the start and walked there, we got to see the Elites starting and stopped at the port-a-loos on our way to our corral (first marathon so last corral). No lines as we selected poncho instead of bag drop-off.
The race itself was good, I'm not sure if the "traffic" was because I started in the last corral but the streets were pretty crowded, if you're trying to follow your pace it can be difficult. Water stops were only on the right side of the street and it would have been appreciated to have them in both sides with paper cups instead of the plastic cups they use. They only have 1 stop with gels towards the end, but I was carrying my own so that wasn't an issue.
The course is easy and flat, and in 2018 I saw people with signs saying world record 2h01 39 so it was exciting to be running in that atmosphere. I had read so many times that you should save your energy and not sprint when you see the Brandenburger Tor but that's impossible even if you know you still have a few hundred mt to go. I finished the race with so much energy from people that I could've kept going!
Make sure you pick up your beer at the finish line, for the rest... just follow the people and you will find everything you need.