What a good topic, much like you I have also thought about a Tattoo. However what seems good right now might not be the same design I would like to see the rest of my life. I have had Henna done, which is really fun. This may sound strange but when the henna was applied to my skin it was sort of a rush. I guess it the thought of getting tattooed but with out the permanent factor. I have never tried any of the home kits. I was afraid they would be too messy and even with a stencil I am still not the perfect artist. This is why I decided to go get on e done by a professional henna artist. My design was a curvy vine which wrapped all the way around my ankle. Nothing real big just simple. As for the henna, it lasted for about three weeks before it started to fade. The trick is once the henna paste is applied try to leave it on overnight with out taking a bath. The longer the paste dries before removing it the darker the design will look. Also it is important to note real henna paste is brown and fades to a light orange color. The reason I mention this is because there is black henna, which is bad news, because it is basically hair dye which can possibly burn and scar the skin. Good luck keep us informed of what design you do and how it goes.
Have a nice day