If you already have a NDS flashcart then I would suggest you just go CFW. Its a bit more complicated to set up than PSP or PS3 were, but not overly so. As for whether to get a JAP console instead of EUR, it depends. There are a lot of tools now for playing region free stuff, so your biggest issue will be with language. I have no idea if you can set the system to use English for JAP consoles, or any other language for that matter. I do know there are a few guides on converting a JAP console to USA, so I assume converting one to EUR is possible as well. Cost wise I have no idea, but don't forget to consider shipping costs when you look at prices.
So I did a hell of a research and <9.2 N3DSs are nowhere to be found and the only few ones on ebay are already at the cost of a PS4 + I ll have to pay huge custom fees to import them from the US.
It seems like me only real option right now is a Japanese import. Do you have any links or places I can read up on converting a Japan 3DS to an EU/US one? I cant seem to find anything relevant on gbatemp.