if your filter doesn't have a pop-up to let you know when it needs cleaning, i would clean it every couple of months or any time you notice diminished water pressure coming out of it.
Depends on what kind your talking about.It actually does not control it is a reducing valve by use of diaphragm and spring tension setting in most applications
A regulator can adjust the pressure setting and a reducing valve is much more restrictive in its settings think of an Oxygen gauge compared to a hydronic boiler feeder