It appears that there is no known limit to the amount you can get in a chain, however common sense (or the very little GF put into it) probably means if there is a limit it won't be very high, and the chances of hitting it are slim. 3-6 seems to be around the mot common, though again I am being vague sorry.
Again I am most likely wrong. Here is the page to Join avenue on bulb so look through it at your own leisure.