I wonder about something that I'm a bit afraid of : what will happen if I bought the game "at this version", but then a new version of this game is available? Will I be forced to buy the "new" version even despite I've bought it?

no!!!!

if you buy the game, you have it and any future updates. what I'm likely to do is raise the price of the base game later on, but if you bought it, that's not something you have to worry about 

I see, thanks for clarifying this thought I had!