Re board length a rule of thumb I've seen says board length= total jointer bed times 1.5. I have done twice the jointer beds but wouldn't want to go longer without infeed/outfeed support. I had an AMT (imported cheapy) benchtop but not for long; I was off to York PA. for a Bridgewood 6" jointer. The AMT was just too flimsy with a screaming universal motor. The newer heavier benchtops like the Grizzly might be fine, I've never seen one 'in the flesh' nor used one. You're right about cutting to rough length before flattening. When I first got my current Jet JJP-12 I tried flattening an 8' poplar board. I got it flat but by the time it was flat the center was 3/4" thick, the ends were 3/8" thick. It's good to experiment on cheap stock.