Hey Jazz, I'm MJ and currently the proud owner of these characters
For Seth as he's a professional photographer then he is likely to have been hit up by Theo for photographs and other stuff he can use for promotions etc at Ink Master. I would say Arden and Daniel, but both their establishments are supernatural creatures only so humans (for Tooth and Nail) not allowed and only humans in the know (for The Looking Glass), but he may endear himself to them both in good time. I'm thinking that there's a possibility of Silas becoming some sort of fitness tattoo model or something (hand wavey stuff) so... possible connection there? Han used to be human until... well, the biting stuff happened.
As for Hux as a merman then he is definitely able to frequent The Looking Glass and Tooth and Nail so clearly he'll have to meet my owners, fighters and managers! Gym wise I know Silas and Han like to keep in good shape so they're likely to be regulars. Daniel too, but he's more of a runner acrobatic martial arts type than a work out in the gym kind of guy.