Q1 - I keep Omni Off because I find that it helps me from rolling when I’m trying to slide into cover in certain situations.
Q2 - I too have been experiementing with the controller remapping, specifically trying to use the Alt control scheme, but remap the buttons to how they are in Default. There seems to be a delay when trying to wall bounce, saw a YouTube video on this and it seems to help some. However, when playing Horde, there are some issues with what buttons do functionally, whether they are supposed to or not.