Originally Posted by PulseArray
Renting a dedicated server would be more expensive in the long run which I don't want. I don't have a business plan because it's a personal community and not a business. If I needed an upgrade I would just buy new hardware. I can certainly up my power allowance.
This depends on what your idea of long run is. You're best to find a dedicated server of comparable or equal specs to the one you want, and see what it's going for each month with a good host (remember, network is important here since latency is key) to compare. Colocation may be cheaper with a budget host in the long run, but not necessarily on a good network. Colocation also incldues your misc. costs like remote hands, replacement of hardware, installations, etc.
Also keep in mind technology changes fast, and so do resource requirements for game servers. It's almost always going to be cheaper to upgrade to a higher power dedicated server as opposed to upgrading individual parts in your colo'd one. This should also factor into your costs as you don't want to be running a dinosaur two years from now because you made the wrong decision initially.
A few years ago, your decision would be unquestionably correct if you could afford the machine outright. Today the game has changed and colocation really only caters to those larger, cabinet+ type clients.
Alas, that rant is solely for a cost point of view. As for your actual questions:
Processor: i7 works
RAM: 8GB+ for what you want to host (TF2 will be a memory hog). It's cheap enough where you can go the extra mile, this will help a lot
Motherboard: Anything SuperMicro
HDD: Gameservers aren't terrible read/write intensive, you can get away with 10kRPM drives.
PSU: Usually will be included in chassis
Chassis: SuperMicro SC811 or SC812