1. Depends on the width of the trough and the angle they're at. You don't need a huge pump for that, but err on the side of being a little more pump than you have to have. You can always tilt them just a bit more and have faster-flowing nutrient solution.

2. A filter on the inlet of the pump is necessary to protect the pump from clogs, and having another filter between the drain end of the channels and the return to the reservoir (like a simple piece of cloth that the water pours through as it returns) will help cut down on the work either filter has to do.

Watch the filters, keep them clean, and they won't restrict solution flow too much.