need to be able to custom cut thin walled PVC pipe indoors

To cut it, they have a hand held PVC pipe cutter that is essentially a knife combined with a holder and two grips that you squeeze. That will give you clean cuts. To make a hole, I haven't done that, but I would try using a heated pointed object, eg nail tip, to first make an indentation as a starting point, then use a hand held drill.

The PVC cutter works fine on that pipe if it is new/sharp. You can do more detailed work with a burr tip on a dremmel tool.

If they are new pipes, a sharp PVC cutter goes right through them but once they get old and brittle, like you find under a sink, I agree, wear eye protection because they will shatter.

First ask if you have to use the thin stuff. The Sch 40 is a little more forgiving.

But you won't cut that with a knife either. Can't be done.

You either saw it (the finer tooth the better) or use a tubing cutter. I use a tubing cutter and get very clean cuts but I don't cut anything bigger than an inch.

Holes. Drill bit or hole saw depending on size. Make sure you have the pipe held securely.

Depends on what you call a knife. A simple handheld knife, I agree won't work. But there are hand held knife based PVC pipe cutters that work like a set of jaws, with one side being the knife. It has a ratchet type mechanism and when you squeeze it forces the knife through the pipe. Works for PVC up to about 1.5".

I hear that CPVC pipe used for hot and cold water plumbing is very brittle but drain pipes are normal PVC which I would cut with a hacksaw.

It is pretty much the same plastic and it all gets brittle with age. Sunlight hastens that if the PVC is not UV protected. You can almost tie a knot in a brand new stick of sched 40. It will certainly bend more than 360 degrees without breaking.

I'm drawing a blank on the proper name. It's just a piece of thin cable with loops in the ends. One saws through pvc by pulling the cable back and forth. A hose clamp might work for a guide.

The best way to cut PVC is with a ratcheting PVC cutter. Some of them are junk. I got a good one on Amazon for 19 bucks a couple years ago. It unavailable now. Cut some pieces of 1 1/2 inch with it for a sump pump project. But I did fine before that with a miter box and a backsaw.

JBI posted for all of us...

What direction are you cutting it? Longitudinally or cross section?