Career Advice: Plant Biology, Entomology, or Microbiology?

I will be starting at UC Riverside soon as a Microbiology major and I am very interested in Plant Pathology. Luckily, the university has a great plant pathology department and the professors seem very open to letting undergrads in to their labs. The dean of the college I am in told us that some of the plant biology and entomology faculty have a very low student to faculty ratio, so those are probably my best shot for mentoring or research experience (although you usually need a year of chemistry before getting a position in a lab). Although upperclassmen have assured me that it is very easy to get into a lab as a sophomore or above, I am having trouble figuring out exactly what area of research interests me.

I am also now rethinking my major. Since I was a little girl, I wanted to be an entomologist, and recently I have become more interested in plants. I originally chose Microbiology because during high school I thought I wanted to go to medical school and be a pathologist and I thought Micro was very versatile, although now I have 100% realized that is not what I want. (Mainly pressure from my family.)

I basically need advice with regards to the following:

1. How should I approach faculty for mentorship/internships/shadowing? (I will be a freshman this coming Sep so I will not be in any of their classes.)
2. If I wanted a career in Plant Pathology, what major would be most helpful: Microbiology, Plant Biology, or Entomology?
3. Should I do a minor? (Microbio, Plant Bio, or Ento)
4. What should I do after graduation? Grad school?
5. Are there entry level jobs in either Microbiology, Plant Biology, or Entomology for someone with just a BS degree? If so, what would those jobs be like?

I realize that these are a lot of questions, so thanks in advance. I really would like a better idea of what I will be doing so that I can make the most of my four years and also just for some peace of mind.