Pulling a feed from a sound board doesn't usually result in a good audio of the music. The reason is the board is mixed for the acoustic characteristics of the house. In other words, it's balanced to make the music sound good in the building it's in. Sending that mix out to your H4n will likely result in a fairly horrible music mix for video purposes. Not saying it can't be done. It can, if everyone involved knows exactly what they're doing. Just pointing out that it's not as easy as it seems.
The H4N is quite often used by musicians and bands to record their music. You may not need to go to so much trouble.
First, try to find a 'sweet spot' to place the H4N where it will record the whole band at once. Record them playing their song. Then listen to the recording on something with decent speakers or good quality headphones. If done in a decent room with good ambience and no distracting noises, this may be all you need. It should certainly, at the very least, provide you with a good foundation upon which you can layer separate recordings of some of the weaker instruments. You may have to play around with the positioning of the H4n to get the best sound.
Plugging the various instruments into the H4n to record them separately is likely to give you huge headaches.
This is a VIDEO project, right? Not a project for some audio engineering class? Don't try to be an expert audio engineer at this point. Get a decent track of the song, and then get to work on the video part. If it turns out well, then you can always later go back and try for a better recording of the whole song.
