oi,
it sounds really great what you are doing, not long ago I was also on a trip "around" Europe, and it was amazing. I have seen that you already visited Barcelona (my hometown), and perhaps you have tasted spanish/catalan food, I actually think it's one of the best places to eat and not too expensive (depending on where you take your seat ofc).
I have been in NL, Germany and Poland, and for sure I recommend you to visit NL, you can find train tickets (DB-NS international) Berlin-> Amsterdam for 39€. I would also recommend you Poland, especially the coast (Gdańsk, Gdynia, Sopot..). Poland really is cheap for most of people who come from abroad.
Not only trains are expensive in France, actually everything is, it's one of the most expensive countries of EU, (also Switzerland, Norway). I would also recommend Copenhague as you are also close to there, so you have the choice to move in three directions; west: NL, east: Poland, and north: Copenhague. (Denmark is not too cheap, but it isn't excessively expensive.
No, AC is legal.
We're so smart that yeah, we make others pay to do their needs.. but if you are smart you can always find not so known parts from the city you are in and find little malls where they have free restrooms, or you can just find a bar/restaurant and use them there, no need to take a drink or sth, and if anyone tells you that you need to, leave and try another one, I've done that plenty of times.
enjoya the trip