Hi,
I tested the second question (i.e., max.size of the reg-exps that contentFilter read) by generating 1500 random strings (each with 26 characters) and pasting into the "patterns" textbox. I then manually wrote a few extra entries with more normal reg-exps. Saved and logged out, and then logged in again.
The first and last strings in that long comma separated list is filtered as they should. So the max is at least larger than this (40559 characters long, including commas).