As to air printing, if it thinks it's feeding, but isn't, check to make sure your filament isn't jammed up some where. You should be able to pull it off the reel with just a little force. Pull off a few meters in the direction of the extruder where it encounters the issue, and see if it sticks. If it's smooth the whole time, then the extruder itself might be jamming. Check you're using the correct temps for the filament. This may be the issue, as you seem to be jamming after about the same amount of time. You might have heat creeping up the extruder head. Look into cooling options for your head if lowering your temps won't work.

As to hollow prints, just adjust your infill settings to change the interior support.