As Houghy said you need to balance the scope as best you can so the gears aren't fighting the weight. It should handle the weight as long as it's balance.
I think it's very difficult to use a DSLR for planetary imaging though.
As for focus - it's basically a trial and error excersise. Take multiple images adjusting the focus as you go.
The hard part is that you can't really use the view screen to get it exact.
The Canon rightangle finder is very useful as it clips onto the viewfinder and magnifies the image at 1.25x or 2.5x but it's expensive.
Image below:
http://www.iceinspace.com.au/forum/a...achmentid=5651
Cheers