The most I've taken is 2 at a time. There were times where I could have taken 3 or maybe 4 if I pushed it, but 2 was comfortable with a full-time and stuff. It all depends, some classes really make you bust your ass, while others you can get through in a breeze. If you're taking something like Calc. and Microeconomics, etc. I would not try to take anymore since it'll be taking most of your time, but if you're just planning on taking easy electives and stuff, then feel free to take more, if you've got the time to dedicate to it. Taking 2 classes is a nice load with a full-time job, but 3 is not bad either, depending on what classes they are and how much work is required in each.