1) Generally colocation provides you only with the following: rack space, electricity, and cooling. If the datacenter offers their own network, you will pay extra for using their bandwidth. All sever equipment must be provided by you. You can get server equipment from a server builder or websites like: provantage, superbiiz, newegg, ect.
2) If you colocate servers and someone whois' one of your IP addresses, it will display the information of the network you are using. Just as it does now assuming you rent dedicated severs from a hosting company.
3) One major benefit to colocation is that if you live close to the datacenter you can actually have physical access to your equipment in the datacenter. You can swap/upgrade your server's equipment just the way you want it. Colocation is often a cheaper monthly payment then renting a dedicated server from a datacenter. However keep in mind you will be paying $xxx - $x,xxxx to buy the servers outright.
4) It depends on the server you are looking to colocate. Each rack mount server chassis is measured by the "U". You will need to find out how many U's your server chassis is to find out how much rack space you will need.
Keep in mind that with colocation you *must* provide your own spare parts. If a hard drive fails in your colocated server the datacenter will not provide you with a new one. Also, if you don't live near the datacenter where your colcoated server is and you need the datacenter to do a task (swap hard drive, install ram, troubleshoot, ect) they *will* charge you. Remote hands usually goes from $100-200+ per hour billed in 15 minute increments.
