Drawing tools select their own sheet by default, so users won't have to manually set the sheet before using a tool (Nor needing to know which sheet to pick).

You can manually change the sheet of any entity using either :CC2MCHANGE: or Move to Sheet (right click :CC2SHEETS:)

If you aren't doing it already, remember that relative coordinates are your friend when pasting with regular intervals. Since the next paste is relative to the previous one, one can mass paste by using the exact same relative coordinates multiple times in a row.

Not directly. I recommend drawing around the settlements with the tool, then placing individual trees after that along the edges to give a tighter fit (And finish off with a sort symbols in map to arrange them properly.)

There is also the exclusion commands, this allows you to specify areas to exclude, but this only work with polygons, not symbols.

There is a bug with a few of the Cos3 templates. You can grab an updated version of the installer from your reg page, or download the fixed templates only from here. That should hopefully fix things for you (note that fixed templates means it will work properly on new maps crated from these. For existing maps, I recommend just copying things over to a new map once you have confirmed this fix works for you)

Your map is 250 by 200 feet, so that is 50 by 40 squares. Each square in FG is 50 pixels by default, so should be 2500 by 2000 pixel export if my calculations are right