Windows Server 2008 R2 Exchange 2010 – Hard Disk Configuration Recommendations

I'm planning to buy a Dell PowerEdge R710
2 x Intel® Xeon® E5620 2.4Ghz, 12M Cache,Turbo, HT
16 GB RAM
Windows Server 2008 R2
Exchange 2010
150 Exchange CALs

PERC 6/i SAS RAID Controller, 2×4 Connectors, Internal, PCIe,256MB Cache,x6
I'm not sure how many hard drives I'll buy or how I'll configure the arrays

The environment in question will only have a maximum of 150 users for the next few years, and their usage is light to average. Many of the users aren't allowed to receive or send email outside the domain. The environment is a production environment but extreme high performance and extreme high availability isn't necessary I'm just looking for something that works well. For reference the current Exchange 2003 server which is being replaced is a 5 year old single core 2 MB RAM server with a single 250 GB hard disk which is still meeting everyone's performance expectations.

The documentation I've read recommends I put the OS and Software on one RAID array, the log files on another RAID array, and the mailboxes on another RAID array, etc.

Arrays:
1. Windows Server 2008 R2 and Exchange 2010
2. Logs
3. Mailboxes

Is this environment too small to warrant setting up multiple RAID arrays like above? Should I just set up the server with a single RAID 10 array and put the OS, Software, Logs, Mailboxes, i.e. everything on the single array?

Should I set it up some other way? Three RAID 1 arrays perhaps for the three separate items listed above for instance?

The RAID isn't intended as backup. Acronis will be used for backup.