Oh dear, remember the days when i was crapping myself about a college portfolio.
Anyway;
Hardcopy, colleges wont accept an online portfolio, they will want to most likely interview you and for you to bring your portfolio along at the same time.
Pictures, there are no maxs, but put in your best work, also i would suggest a few examples of your post processing work flow. Finally, some comments definately on your pieces, and depending on the type of work, also look at doing idea sketches, ie if its a set piece of abstract/conceptual photography, or possibly a panorama, keep in mind that they are going to want you to explain it, and if you have the shots set out with your work flow, concept sketches and some self criticisms of your own work they are going to like it all the better.
Wracking my brain trying to think of the last few points.
Oh yeah, since its for college, try and get a variation of mediums in there, prove that you can use your camera in more than one area, main ones i would aim for are landscape, sports and portrait (which is nicely backed up by fashion or glamour photography). You may want to look at if you can get some concert photos (low light really) in there, just to have it.
Also, one last point, when noting your photos, i would suggestion mentioning, how you took the shot, exposure, setup, etc etc.