This question is to varied to provide a proper answer without knowing more. I like the approach of looking at the requirements and providing the hardware to meet those requirements. I can think of plenty of machines running in datacenters that for whatever reason don't require a high level of redundancy and don't have redundancy built in. Not common, but it does happen based on need...

for instance aardpsymon where the hell does heat management come in?
Start dealing with a datacenter that is over 50k square feet with over 5,000 servers and heat management becomes a huge deal. He has no clue what kind of environment the OP is in, so talking about heat management for servers is an important aspect of proper management of a server environment.

I have servers that require 4 HBA's, 5 NICs, 8 Internal 15k RPM SCSI drives, as well as two external fiber networks. One for backup and one for SAN. SAN enclosures requirements can get even crazier depending on the IOPS and overall system load. Point being that what defines a minimum server is the requirements for whatever is going to be running on that server. There is no right or wrong answer.

As far as the question around tape drives it depends on what kind of tape drive you are using. LTO-2 drives can store 200GB and approach 1.8GB/min. Far faster than you can get with a dvd drive. LTO-6 drives can store 3.2TB and approach 16.2GB/minute. We usually require atleast LTO-2 drives for machines with very large databases. My new environment will have dramatically larger databases than anything I've backed up before and we will probably be using atleast LTO-3 or 4 tapes along with extremely large disk enclosures dedicated to VSS snapshots.