Honestly, expect shit to go wrong. Sounds like you’ve gotten all the important shit done. You’ve got a plan, you’ve been working towards it for a while and seems like your partner is into it as well.
We had a similar trip a few years back, first time overseas for some of us. Lots of planning and preparation went into it. Then our trip planner fucked up one of our bookings in Paris. Meaning we almost missed out on doing some tour that ended on the Eiffel Tower. A couple of times trains were missed/delayed.
The only times the trip strayed away from being the fantastic trip it was is because people let small (and sometime not so small, to be fair) disappointments or missed expectations turn into high stress/anxiety events. You’re going overseas, shit may go wrong; be ready for it and be cool with it (while also making sure you have travel insurance). Also take time away to do shit yourselves that the other may not want to do and always have set meeting times and locations to check in if you do.