guitars

When you can play songs and your rhythm is confident.

If you're looking at this from just starting out, you need less than you think. If anything, it is easier in a band, because you can rely on other people to hold the thing together, if you take a momentary breather. I spent years mentally flagellating myself because I couldn't play a lot of Grateful Dead tunes the way you hear them on record, and it should have been obvious but was not that that is because there's two guitar players. A lot of Garcia's lead bits would sound weird and not quite musical, without Bobby under there keeping the rhythm going.

Mostly depends what music you wanna play, but in nearly every genre there are the complementary talents of leads/shredding and chords/rhythm. Ideally you have both, but the band sounds best if everyone is aware of what everyone else is doing in the song. If you like Blues, find another Blues player, and get together to jam, in which you pick a riff/progression, and trade off between soloing and rhythm/chords. Middle step between a full band.