I think it depends on what the other courses are; if they are math/science/heavy duty type stuff that requires a lot of homework and are not based on any knowledge you may have (like history or English comp courses, you could "wing" those in a pinch if you have adequate background) but taking too many labor-intensive courses at once will just get you frustrated and burnt out when you need to take a bit of a break but can't find room to do so? You can write a history or English paper over time but you can't do a "problem" over time.