I am a terrible programmer but have done some ISR routines that also do things fast.

If I can do it, everyone can do it! Try it and see how it goes. After all we are still here...

I'd select a PIC of relatively recent 18F series so the famous DT INTS-18 will support it, follow the instructions for the DT INTS and do some test. See here: http://dt.picbasic.co.uk/INT16/DTINTS-18

Nothing to be afraid of.

Ioannis