I don't think that separate recorders are the way to go.  Rather, some sort of multi-track audio recording device would be far better.

I guess it really depends on how much the music matters to your video.  Double system is definitely the way to go, but unless you really know what you are doing on the audio side, a good capture of a band playing live is not for the faint of heart, and this is coming from a guy who does exactly that for a living.

You will need at least one, but preferably three camera operators, and you'll need someone to focus on the audio if you really want to do it right – especially if you decide to mix it live-to-2 as opposed to multi-tracking.  IMHO and YMMV

watch videos of bands that you like, and then ask yourself "what shots will I need?  What angles?  How did they get those shots? How is it lit?"  You can learn a lot just by stealing with your eyes.