New Dell Poweredge 2800 Configurations

Hello everyone
I am about to buy two new Dell poweredge servers.
Servers will be running AC, DNS, DFS, IIS (local intranet site), NLB. Will be also used as print, file servers.

Here are the specs for the servers.
***PowerEdge 2800 (two of them)***
-Dual Xeon processors 3.0Ghz/2MB cache
-5GB DDR2 400Mhz RAM
-Hot-pluggable Split backplane
-1 PERC4/DC, 2 Internal Channels, 0 External Channels controller
-2 RAID 5's
1) 73GB 10K RPM * 3 = OS
2) 300GB 10K RPM * 4 = Data storage

Questions:
-Cluster or NLB these servers? ( for 100% fault tolerance)
-2 RAID controllers? or just one? (1 for each RAID5)
-I am planning to buy another two servers later on wich will be running MS Exchange and the data will be located on these two servers I am buying right now. Is that a good idea?

Any help would be greatly appreciated, thanks!