This kind of thing work best when artists team up. It’s way easier to promote a “Studio Tour” event with a bunch of artists in close proximity who can all pitch in to print posters and send out the invites to their own respective networks. Appointment only works when you have dedicated buyers. If you have plenty of those reaching out to you, go ahead. If what you need is for people to be able to casually peruse the work while thinking about buying, that is what your gallery does. Have an opening to chat with the clients for the VIP treatment.