As your guest is a “newbie” too he might be a bit unsure on what’s constitutes acceptable.
The best advice we can give when it comes to guests is to be crystal clear from the off.
Never assume they will know what to/ and what not to do - you will be surprised how easily guests can misinterpret and misunderstand things!
Clear house rules are key, make sure guests read and accept prior to booking and again on arrival. Keep the tone light, you don’t want to scare them off or make them feel unwelcome. But make it clear that maximum occupancy is 1 person and for security reasons you ask they do not invite people into your home during their stay.
The couch thing can be resolved - if it’s a shared living space just mention you would rather him not sleep in his room, just say you aren’t a good sleeper, so sometimes come down during the night to sit on the couch and read (hopefully he will get the hint)!
Hope things go ok!