When it comes to tattoo, I'd say a typical Greek design, like the ones seen in vases and jars if the time would be a good fit for Asterion. I think Also, stars, the Taurus symbol or thunder would fit his mythos. On the other hand, maybe crisscrossing lines or a word in ancient Greek he feels particularly attached to.
When it comes to nipple rings, I can thing of the stud type of nipple rings, nipple rings with chains and ones with axes or thunders on its edges. More tribal versions would be cool too.
When it comes to fur colors I'd back gold and other colors.
Thanks for all your hard work.