I think that rather than imposing some arbitrary limit upon individual
part sizes, if possible you should use something that would make sense
to a reader. Divide your FAQ into reasonably self-contained parts
bringing together related items.
For example, I divide the soc.culture.spain FAQ into four parts:
+ Introduction
+ Netiquette
+ Information for Travellers
+ Spanish On-line Resources
These vary in size from approx. 10k to 50k.
Similarly, the Perl FAQ written by Tom Christiansen and Nathan Torkington
(which I use frequently) is split into nine parts:
+ General Questions About Perl
+ Obtaining and Learning about Perl
+ Programming Tools
+ Data Manipulation
+ Files and Formats
+ Regexps
+ General Perl Language Issues
+ System Interaction
+ Networking
These vary in size from approx 15k to 50k.
HTH,
Alain