It hosts up to 100 trains a day, so you'll never go long without seeing one. Also, you can shoot the trains from public property. However, be careful. The area between the two northern mains is patroled by CSX police. Be sure to have your camera out and always be careful.
Trains can come at up to four at a time in Porter.
It can be dangerous if you are not familiar with the area. This will give you some info on the Porter PM connection. This is where the Muskegon and Grand Rapids subs of CSX's Pere Marquette trackage meet. If you have any PM questions, I can try and answer them. Amtrak owns the Michigan Central trackage from North of the former NYC mainline after the Penn Central debacle.