heck it depends on the budget and the things that you would be running in the server. For what purpose you are going to have the server? say, webhosting?
you should have the idea about the budget and the average resource consumption by the server before getting one.
1. Cooling.
2. Physical access and security.
3. Remote access, Lights out management, etc...
4. Environmental Monitoring.
5. Fire and Flood control
6. redundancy (mostly network and power)
7. method to physically access data center .. you'd be surprised, at some DC's it took me up to 20 minutes to get in at night because they only had one guy on shift and he has to also patrol and make rounds, not good if a server is down.
It all depends on your server build. You can have basic template and then you can add additional features to it. You need to consider the following options as well:
High Availability
Disaster Recovery
Monitoring
Security
SAN or NAS storage
Virtualization
Backup Connectivity
SAN connectivity
Load Balancing
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