Then you have something to measure from for your three contact points, pedals, saddle and handlebars. Crank arm length is also worth noting, as you might not want to have a longer crank length if your knees are not used to that. Handlebar width is also worth noting, you might not want a narrower setup if you are carrying much of a load on the bike.

As I noted above, in continental Europe a lot of touring bikes have flat bars, thus when renting you might have to look harder to find drop bars. But, if you only rarely or never use the drops, you could certainly switch to flat bars for the trip.

And I noted above when I did a couple trips to Europe where the bikes were supplied, I brought my own pedals, water bottles and saddle. Pedals so that I knew that my shoe cleats would work well with the pedals.