Big questions. number one-If this will be outdoors dont use wood. No matter how well sealed it will warp and pop off the tiles. If its indoors-no problem.
There are different ways of finishing off the sides, Maybe some can describe it, but its easiest to google images of them and observe the edges in the pics.
I searched around and found some faqs and how to stuff that includes tabletops and tiles of different thicknesses. It can be done and thinset will be your friend. Slow is the resident expert with that stuff. Be sure to post pictures and ask more questions! hope this helps.
http://www.expertvillage.com/video-series/98_mosaic-tile.htm
(videos)
http://www.mosaicartsupply.com/mosaicfaqs.htm#Q0

http://www.mosaic-tile-guide.com/how-to-make-mosaics.html

copy and paste into your browser

good advice WW! I'll just add that a flat piece can be made of several thicknesses if you use the indirect method or you can just do it direct then coat it with epoxy resin after grouting.

my advice is a net search on indirect and reverse indirect method. several different ways to do it

Nothing to add here - since I like texture in my work, I use many different levels, and don't ever plan to do anything that NEEDS the resin. I agree w/the above advice from WACKY and NT for your purposes.