Since it's electric, I'd recommend D'addario strings, they're cheap, and you'll want an electric set, I'd recommend .10 gauge. One thing you'll want to do is after you're done playing, wipe down your string with a cloth, it'll help your strings last longer. All you need to attach strings is simple dexterity. I'd ask your local music store if they could show you how, as that's probably the fastest way to learn.
A capo is essentially a clamp that shortens the guitar neck, you attach it on a fret and it raises the pitch of all your strings strummed open.
Picks are purely preference, though I'm sure most would agree that if you're going to play melodies or single lines, harder picks are better, while some find that lighter picks are easier for beginners to learn how to strum. I recommend buying several kinds, or testing out some at your local guitar store.
Good luck!