First. Congratulations on getting your own little place
Second. Ignore all the rules that say a "Man Cave" needs a pool table, big screen tv, huge sound system. Your cave should represent you and your personality. If anyone goes into your place and your not there they should be able to tell that this is the cave of 2fish.
Third. I know you have mentioned you know what you need, but a comfy couch that is longer then you can be a godsend. You may have (drunken?) nights when getting to the bedroom is too much of a hasel. Thoes nights a couch where you don't have to curl up on to fit in so you get a good nights sleep will be apriceated