Panther Mail hardware Questions

Hi, I'm about to purchase and configure a G5 Xserve 2Ghz. I plan to partition the internal 80Gb drive into 20Gb for system + 60Gb for email for 30 users. I have a 250Gb external raid which will be used for file storage, home directories, etc. I have 3 questions: 1. Is the internal 80Gb drive, when partitioned, fast enough to host mail accounts for 40 users? 2. Anybody see a problem with this setup? 3. Am I putting too many eggs in one Xserversince if it goes down I will lose ALL file AND mail services. Many thanks, b.