I think the "remove wallpaper" thing was a left over from the old version of the program. In the old days when computer maxed out with less than a gig of ram and hard drives were under 40 meg and such, the wallpaper being a picture of size COULD make an impact to the system. With todays systems, wallpapers haven't gotten any bigger, but you have much more resources even in a weak computer, so short answer, no don't worry about it
I check "force idle task to execute". If you don't you potentially have a program cued up ready to run taking space. If you force it to run out, it clears up that space.
I don't remember what the selections are for monitored programs, and the minimize while waiting only means that it will minimize AlacrityPC so that you can see whats happening to the "monitored programs". I wouldn't worry about those either.
With your system down to 21 your in pretty good shape.