confidentialcoll

It varies a huge amount on your priorities, academic background, school (CC or seas), area of interest and placement level (esp seas). give info about these, and you'll get a better answer

if you've gone to a rigorous school and have taken many and tough classes taking 6 is doable, if you're priorities are that you want to party it up and make friends rather than get a head start on requirements 4 would do. if you're taking physics 2801, the physics class on crack 5 is a good upper bound. What classes you take are entirely dependent on placement level, in seas the average number of classes would be 5-6 and CC 4-5 first semester.

an average seas schedule would look like, but of course apart from #1 there are many more options than this:

1) gateway/university writing
2&3) chem 1403 and physics 1601, or phys 1401 and intensive general chem
4) calc III
5)pre-professional course / comp science / principles of econ
6) optional: another from (5) or any other course of interest perhaps in an intended minor.

CC, here 1&2 are set in stone, 3 is highly advisable if you don't place out:

1) lit hum
2) frontiers of science or university writing
3) Language if you don't place out of all 4 semesters
4) major cultures if you can get in / intro class in interested area
5) optional: another class in interested area of study

it all depends how much you want to work, each of those schedules is 30-50 hours of work (including class time) weekly, varying with your preparation, efficiency and achievement level.