Help with the 3ds ( I'm a noob and I need some info before buying one !)

Hello ! So I'm (still..) planning on buying the 3ds and I need some help. I've never owned a 3ds before so I don't know a single thing about one. I'm planning on modding the 3ds when I do eventually get it. 

Which 3ds is better? A japanese one or a USA/Europe one? What problems come with the 3ds being region locked? C
an I play with other people if I have a 3ds from another region?
Can I fix those problems with modding it? Which can I not?

Can I play japanese games on a USA/Europe 3ds and vice versa?

How does the 3ds from Japan affect the language?

What are some important things I need to know about one before buying one?

Thank you! :)