There are two places to learn about PerlRun: the mod_perl Guide and the mod_perl mailing list. If you ask a specific question on the list, you will usually get a useful answer, but read the Guide first if you want to avoid RTFM answers.

There's not that much difference between PerlRun and Registry. PerlRun attempts to clear out all globals and subroutines created without an explicit package in your script. Otherwise, it is isn't much different. It sounds like your main questions are general mod_perl issues, and not PerlRun-specific at all. So, ask away!