Well he wants to look like you- so that's your template.
If he's bringing this up, then he's in the driver's seat and he wants to get closer to you- so you might be surprised by what he comes up with.
I think you're getting into a very touchy/feely place to go here, so I'd say it's up to you and how much of a bisexual tone you're willing to set in the household. Since he's family, (and you're close to his dad) the trail back to the rest of the family is immediate.
I'd say you are safe to "show and tell" and allow him to see you naked (in your house) and offer him all the resources (razors, shaving cream, etc) for him to take care of himself. If he asks for your help, go slow.
There should be a mutual level of risk and mutual level of trust. Let him see you naked and then let him show himself naked to you. Let him discover you watching a movie that is not family friendly, and then allow him to reciprocate. With each step you take towards investing in the relationship you have with your new friend/family/roommate you should see an equal investment from him. Before you force anything that seems like you are manufacturing something that you have in your head- after a time you will know what he wants/expects from you as a landlord, as a cousin- and as a potential role model.
Keep us posted.