Should you chamfer CPVC pipe before gluing?

About the only reason I could see to chamfer the end is that it would seat a mm or 2 deeper in the fitting. In that the glue is solvent welding the plastic, I doubt it makes a lot of difference in the strength of the joint. That said, I don't see that it would be a problem if it helps in joining unless you overdo it (like sharpen the end).

As far as I know, primer and sanding serve the same purpose - primer softens the surface and sanding gives more surface area. Both of these improve the performance of the solvent. Whether you need primer or not depends on the glue - there are single step glues that combine the primer and cement and there are two step glues that require priming then gluing.

I have owned one for years, it aids insertion and helps remove tailings that otherwise would flow down the line necessitating more thorough flushing (or maybe plugging something up). It's a good practice but no requirement. As for CPVC cleaner or primer, follow the directions on your can of cement.

I can't see any advantage to chamfering the ends of PVC pipe, before applying glue and inserting it into the fitting (elbow, tee, coupling, valve, etc.) Where the pipe "dead-ends" into the fitting, the fitting's "stop-shoulder" is cut at a right-angle (not chamfered), and the end of pipe after cutting (without chamfering) would also be at a right-angle.

So all you would be doing by chamfering the pipe, is reducing (very slightly) the PVC-to-PVC contact (a small 45 degree angle "gap"), once seated.

Admittedly, after having said all this, the effect is probably insignificant, as the "lip" of the "stop" inside the fitting, is a fraction of the wall thickness of the pipe, providing little in the way of PVC to PVC contact. The system is obviously designed to satisfy the requirement via thorough application of glue between the external circumference of the pipe, and internal circumference of the fitting.

Most important is to ensure a right-angle cut on the pipe. I use a mitre-box and saw when possible. Then, even with clean new pipe, with a fine grit sandpaper, sand lightly the pipe-end circumference to a length equal to the depth of the fitting "stop".

Also, "scrub" lightly the cut end with sandpaper on a hard flat surface, or with sandpaper glued to a block of wood (without taking the end "out-of-square"), to ensure cleanliness and maximum contact. Then, wipe where sanded with a clean rage, and make-up the fitting with the glue per instruction, ensuring dead-end contact with the stop-lip in the fitting.