Should my resume fit on one page?

Don't think in those terms to start. Just write your resume and see how it comes out. If it's like 1 page + 5 lines? Probably easiest to trim it to 1 page. If it's like 1 page + 20 lines? Go ahead and fill out the second page. On that first cut, don't put stuff on there just for shits and giggles, but don't hold back either. The point is to let it be somewhat organic.

Should my resume only include my professional experience & skills?

That depends on what your "other" experience is. I know for a fact that I got my third job because of a certain hobby... They were willing to pay me to do stuff I did for free on weekends (Oddly enough, I dropped those activities as a hobby but I loved my job!).

What info do I include about college?

University name. Degree name. Year of graduation.

Should my GPA from college still be on my resume?

No.