SMF also has a support board I see. I might be able to get some assistance there.
Before I did any moving I'd convert the layout to be as close to what it would look like on the new board, as well as the settings too, to minimise any "trauma" for my members.
The cost seems like it would be my biggest issue but I still don't have any idea what it'd be. I posted on another forum asking about how much ad revenue a board this size could expect to earn. Hey--if I can make any money on it at all even a little that would be a huge incentive for me to pour even more effort into making it grow more.
Oh--Another thing I thought of. Is it possible to set up the forum's settings, skin etc. and stuff BEFORE porting over the cloned boards/threads/members?