"A bit like a youth hostal, but for adults."
What you are describing isn't "like" a hostel, it is a hostel. Hostels these days aren't just youth hostels, lots of adults stay in them. Nothing wrong with that, there are other Airbnb listings that follow the same model. And I would advertise it as such. There are also online hostelling sites that you could advertise on, so you'd be attracting the type of guests who enjoy that.
Emilia has pointed out the things you need to be aware of when undertaking a set-up like this. I would add that you might consider that rather than renting 6 rooms, you look for a live-in manager who would be responsible for making sure it all flows smoothly and keeping the common areas clean, who would occupy the 6th room. It would be good to have someone in residence who is a good "people person" who could smooth things over if there are guests who aren't getting along with each other. A friend of mine runs a small hostel in my town and does this and it works out quite well.
@Ellen-and-Todd0