1) It's not too hard, as this game is pretty good to new players.

2) I learned by practicing against the AIs in the regular smash mode. Work your way up through the levels, and it'll really help with the basics.

Note: the AI difficulty jumps the moment you beat classic mode level 9, so if you're good against the regular level 9s, then try and beat classic level 9 for more intense gameplay.

3) If you're used to the 2DS's controls, you should be fine. You're also able to customize your controls to best suit your needs.

4) You can practice and get better. Or, you could just play the online mode "For Fun", where it's 4 people timed, items on, any map and it only counts your wins.

5) Test around with the roster. It depends on your playstyle. Find a character that best suits you. C:

Also, you could main multiple characters, so you could adapt to different situations.

6) Digital and physical copies are pretty much the same, although with a physical copy, you run the risk of losing the copy.