Flux core wire?

The issue you may run into trying to run a 10lb spool is the drive motor on the harbor freight one not being strong enough to pull it around.
This would probably be the case. As for wire go with .030 as it is the smallest diameter flux core wire you can purchase and this machine only has 125 amps on its best day. You will run into the duty cycle with this welder. Buy the Lincoln 211 wire at either Home Depot or Lowes. By the way I'm a welding instructor and have been a welder for more than 30 years. Also as said above buy a quality hood. At the college I teach at we highly advise to not use the HF hood.
Kevin