Sizing Linux Partitions for use with Postfix

[Jon]

I want to create a new debian Linux based postfix system to sit in front 
of Exchange 2003 and act only as an SMTP gateway for starters and 
possibly do some filtering down the road. There seems to be less than 
65,000 connections per day coming at Exchange and I'm thinking to start 
with one ~16 GB disk for the system.

I've read bits in the list archives that /var/queue and /var/log might 
be advisable to live on separate partitions. Digging around more and on 
the list and Internet I'm left wondering how to go about carving up an 
appropriate disk layout or calculate how much I might be safe to 
allocate for 'queue' for a new (low volume?) system? Is there any wisdom 
anyone would be willing to share, pro's con's, etc. to help proceed?

thanks!