Crew needs to be fit or at least have endurance. The sheet loads can be quite a bit if the wind is up.

Single handing the N20 is possible but not idea. Min crew weight by class is 325, and most people seem to put at least 360 on the boat.

Also note that you wont be able to race OD with the N20 sailing single-handed. IMO, there are much better boats out there if you want to single-hand. The N20 was never meant to be that boat.