Like you, Machka, I'd done a lot of camping and cycling before touring, also combined the two where I camped and cycled out each day, so I kind of knew the ropes. I also cycle practically every day, and so know my limitations.
I did a few 30 mile practice runs with my friend before first tour, but that was more for my friend than me, and I cycled my daughter too and from school, which, though a shortish run, certainly built up the strength.
But still, the first few days on tour were a bit of an eye opener, but not so much the excertion of the ride, as the constant getting lost. It took us a while to get to know the way of foreign cyclepaths, and the need for constant checking we were still on the right one.
But it all made for a great story when we got back, and I don;t think I;d change it if I could.