The low cut helps remove some of the wind rumble noise outdoors, but also chops off all the low bass content from what you are trying to record at the same time. The resulting recording will sound thin and weak. It doesn't even really remove all the wind noise completely, just the worst of it. It can sometimes be used to cut bass from obscene over-driven subwoofer content, but is not the most appropriate tool for doing that. And that won't be a problem for what you are recording anyway.
You won't find anyone here ever recommending the use of ACG. And you almost never want to use the low-cut on the recorder. It's always better to do that afterwards if necessary, but you won't need to do so for what you are recording.
I think the mic-gain switch only effects signal through the mic-input jack, but could be mistaken. Here's more detail if it does control gain when using the internal mics-
Put the recorder in record/pause and adjust gain while clapping loudly using the buttons on the side to get good levels just under clipping. If the side-button controlled gain is anywhere around the middle of the total adjustable gain range, you're good..
If you need to set the side-button adjustable gain to less than 13 to get acceptable levels, set the gain-switch is set to low and go no lower than 10, regardless of the clipping indicator light. If you need to set the side-button adjustable gain to the highest part of the adjustable range (I forget how high the numbers go) to get acceptable levels, set gain-switch is set to high and dial in as much gain using the side-buttons as you need.
If all voices are amplified through the PA, get in-line with a PA speaker and not too far away from it where the sound is as clear as possible. If only some content is through the PA, and some is unamplified, sit as close to the stage as you can, but where the PA still sounds clear. If there are small speakers across the front of the stage facing the audience, sit in the front row directly in front of one of those.