Well, I lost my entire post, but if you asking about servers, I would only use Dell or HP. Personally, I would go with the Dell T610 which is the equivalent of the Dell Poweredge 2900, which was "the" server
As far as disk space, of course, get as much as you can as its cheap. It all depends on the RAID you choose, 1, 5 or 10 or a combination thereof. For instance a RAID5 will need at least three drives and you lose one drive of space no matter how many drives. A mirror (RAID1) only needs two drives, but you always lose 1/2 the space. A RAID10 is a nice RAID. But, you will need at least 120GB for the OS and I would get at least 500GBs for data.
The processor is a no brainer as any good server will come with at least two dual core or one quad core processors. I genrally go top minus one or two as that is the price break. As far as RAM goes, the more the better. If you get a 32-bit OS, you can only use 4GB of RAM of which only 3.2 will be used and SQL Express will grab 1GB. If you go with a 64-bit OS (great idea) you can put up to 64GB of RAM, way more than you need. I have 20 which is more than you need, but 12GB is perfect. Then, if you do get a lot of apps running SQL and you move up to SQL Server Workstation or Standard, then SQL will grab more and more of your RAM (what some call a leak -- which it isn't). But, you want SQL to grab a lot of RAM. If SQL is using 4GB of RAM, then AC and Sharepoint and Monitoring and Acronis and any other application you have using SQL will run fine.
Make sure you have a CD/DVD burner and make sure you have USB2.0 and eSATA ports and maybe even USB3.0 ports. AND, have a floppy disk even in 2010. They cost $5.00.
You don't really need a special closet. In fact, you don't need a closet at all. It's better for ventilation. Just put it anywhere.
