ok i have decided to get a normal computer and turn it to a server

i have some quistions=

1.will it take up alot of energy (need to know for energy bill)
2. Will it get very hot
3.How am i going to cool it down
4. Ok i am thinking of using a rounter with it if i do that i will be shareing internet with 3 computers including the server will it slow down performance in any way for the othere computers or the internet speed



ps i have bandwith