Ok so ive had my new build running nicely for a while now. I look to my left and theres a pc just sitting there gathering dust so i decided i want to setup a home server. I do have a couple of questions sue to the layout of my network devices.

Currently the only phone line is in my roomates room(where my modem is located) I have a cable running from the modem into my room and into my PC. The modem has routing capabilities but icant take advantage of it as i dont want to have multiple cables running from the modem into my room (through the roommates room).

What should i set the modem up as so that i can use a router in my room?

Would i have it go from the modem into my server, then the server into a router?

...As you can see im a little confused at this point on where to go. Any advice on this is greatly appreciated.

If the Modem has more than one port, hence can hand out more than one IP address then put a 4/5 or 8 port switch in your room and connect that to the modem. If the modem only has one port then get a router with a built in 4 port switch. Run the line from the modem into your room and then into your router. From there you can connect the pcs to the router.
If you want the access to the server outside of your network you can either set it up in the dmz, security risk doing this, or just open up the ports on the router that are needed for the programs.