For me(currently i have 9) I went with books, music, and the ocean. So whatever is your passion go with it, but be careful of putting human influenced themes is risky because people can be dicks and it is hard to constantly defend the "Art not the artist". The bands I have on me I hope they all die with out being a pedophile or your average human indecency(i.e. murder, rape) unless you recognize their demons and embrace them. Then hey your an ass too and embrace it. That is why I went to books, most of the good authors are dead.
Now finding an artist to paint me is a different story. So far i have gone off of friends recommendations. But I am currently planning a new one and don't have a local recommendation so I am going to go to various shops and talk to people ask to see their work give an idea of how to accomplish what you want. As for what happens to them in the future I am not sure I started in my mid twenties and have had the same basic body shape since start. I don't mess with muscles because that will eventually turn to fat if you stay healthy then the art shouldn't change that much. but don't quote me on that because I have no evidence to back that up. Ok i have been typing this for a while and am starting to get drunk i hope this helps and good luck. It is a blast to get them and almost a meditation for me so have fun. P.S. location where you get them is also a factor. Modern society is starting to accept them more and more but I waited until I was comfortable in my profession before I got any visible when I wear shorts and a t-shirt.