Dell, they have very clear instruction manual on installating Redhat Enterprise on their server. Also nice quality server case (SSI EEB) are hard to find, the original Intel server cases are very expensive, end-up DIY server hardware maybe more expensive than you buy branded server. So don't waste your time spending on testing compatibility on hardwares.
Ram
Ordinary PC ram like Kingston Valueram is not designed for use on 24x7 server, PC ram doesn't have ability to correct any error during data transaction, those error will sometimes occur when you keep the machine turn-on for long time and they will cause all server process become lockup. So you must equiped your server with ECC ram, which include error correction mechanism to maintain your server stability.
Hard Drive
Ordinary hard drive didn't design for your to keep turn on 24x7 and for configurate as any RAID set, I seen many people using ordinary SATA hard drive for RAID1 or RAID5 and end up need to rebuild it almost once a month. That's why most server now a day using very expensive SAS hard drive, which provide same realibility and faster performance as SCSI hard drive. For cheaper solution, you can buy Enterprise version of SATA hard drive e.g. Western Digital RE class hard drive, this kind of SATA hard drive designed for server use, suitable for RAID set and 24x7 use and not much expensive compare with ordinary SATA hard drive.