I would start very much where Gutbucket suggests and record with your H4N at the front of the stage pointed at the band (maybe from down low behind the vocal monitor angles up to avoid getting them since you'll have vocals in your sbd feed) and send the sbd mix from the FOH mix position (either through an aux send or control room send not sure on that board) to your onstage location through the snake returns.
The idea with this approach is to get complimentary recordings - clarity and detail from the sbd source and room sound from the mic source. The mics will fill in things like guitar amps and drums that are loud onstage but not well represented in the board mix and give some roominess to things that are primarily only represented in the board source like vocals, keyboards and snare/kick. This kinda depends on the size of the venue, if some instruments are DI or mic'd up cabinets, etc... usually smaller venue = less things that are loud onstage being sent to FOH since you can hear them fine in the audience already.
Mixing the two sources is really simple in a free program like Audacity. There's a wealth of threads here about how to accomplish that specific task.
If this works out for you and you want to upgrade at that point you could get a multichannel recorder like one of the Tascam DR series for a couple hundred bucks and a decent pair of condenser mics for a couple hundred. You don't have to spend a bunch to get solid recordings in this scenario. You are kinda in the cat bird's seat since you have access to your own sbd and where to place your mics. If you sprang for a Zoom F6 and a pair of Line Audio CM3 mics you could be making killer recordings for around $800 if you buy used and have a lot of flexibility in your approach.