You got a 40D, just point it at a star and zoom in with live view to focus.
As for sky fog, all you can do is take some exposures and see the limit. I use the EOS software to capture and am lucky enough to do 20 minute subs to the east of here. I don't use filters. I have no idea how long you'll get there.
I do have a mask here and it makes focusing with live view easier, not sure about better
