I read this post several times and still am really not sure what you're doing, or attempting to do.
Where does the blower come in to play?
Why are you putting PMG's on both ends of an axle?
A steel axle just using plastic bearings will wear them out quite rapidly unless you have some scheme of keeping the lubricant flowing. Use good quality long lasting bearings. You may have a higher initial drag, however they will last longer.
As far as the rest,, no clue. Not enough information for me to even GUESS what you could get...
If you're talking about running this "device" from an electrically powered blower..
forget it, you'll get less electricity out than you put in..period.