I have an iRiver H120, Church Audio mics, and battery box. Should I get a bass roll-off, pre-amp, or neither? How much are these? How much will my recordings improve with each? What do each do? Thanks.
That depends. To make a long story short, with your iRiver, Church mics and bb, you're good to go. It's not a matter of what you "should" get, but what you actually need.
Taping heavy bass, booming venues? Roll-off might be a great idea ( bass roll-off filters the amount of bass you are going to tape). Going to tape soft, acoustic type music? A preamp is an excellent idea. The preamp can be used if you're recording device has a noisy buit-in preamp. In this case, you can lower your recording's gain and use the preamp's.
Anyway, you have lots of options. Let you ears ( plus your real needs) be your judge.
Take care and have fun