Guide is on Discord, link should be at the top of your page.
You can buy the cage to hold slaves when you reach a certain level with slavers, you have to progress slave traffickers to get it.
Robin will leave when he notices you interacting with slave raids, or with your personal slave cage. If you have him resting with Dr. Choppy or at one of your guest areas in Nogas, or potentially Greyfold, he will remain unaware you're a slaver & rejoin you whenever you ask. It's still probably more hassle than it's worth to pursue slavers much if you like Robin as companion though, in my own experience.
I think ( not 100% certain) you bought the muscle slave his freedom, since you had nowhere to confine him when you bought him. I've never pursued that route personally though so I might be mistaken.
The Shine Town room is apparently fixed next release. it should be out on Itch in November.
Hopefully some of this helps you ~