Thanks again for all your help and suggestions! I decided against the grout. I did a grouted sample with leftover tiles and wasn't happy with the look. It seemed to "flatten" it, when one of my favorite aspects is the different tile heights. Plus I love the old wood peeking through.
I'm calling it The Potting Shed. I included some pics of my inspiration! Not sure what I'm doing with it yet..I might muster up the courage to enter it in our local museum's member show :) Or I'll keep it!
Picture from MySweetSavannah Blog
Picture from HumbleSeeds Blog