When thieving npc's that give coins, it doesn't open coin pouches which makes it break after 28 pouches are in the inventory. Pouches can't be banked either so it will also break when it tries to deposit the entire inventory. Besides that it's working very well. Hats off.
There is no average number for that, it depends on the skill, the length of your session, the script and probably also the amount of time you play on it legit.