Quote Originally Posted by Bruno View Post
But I guess that having a very old firmware can be real bad right?
For now yeah, game compatibility and online capabilities (specifically the eShop; not sure about normal online play) are an issue when using an older firmware. It's the same problem they had with the PSP for a while, and those issues were ironed out eventually while still letting you play backups. I imagine they'll eventually have it figured out with the 3DS too; it'll probably just take a while.

Quote Originally Posted by Bruno View Post
Since you have one 3DS can I buy all the games in digital form from Nintendo eshop or it's just for some games?
Don't think they have every 3DS title constantly available, but they do usually have a pretty decent selection overall, normally including the newest releases and even some older games (NES, GBA etc, here's a list).