Thanks for the tips folks - "Hire it out" is probably the best, but the die is case, the project is in motion, and well, here I go...
@Jon Bon - I too am never satisfied, and I always hear my father in my inner ear harping about "that's not professional work" - I need to stop carrying his baggage around. He's not a professional, I'm not a professional, of course this isn't professional work. This is weekend warrior work.
That grout knife is nifty doo-dad. I'll look for one at HD tonight. It would likely offer much better control than the diamond blade on the oscillating tool which I have been using for similar tasks. For the record, the Osc. Tool works really well and really fast, and really scratches up the face of your tiles if you slip with it.
@sonofsven - Good tip on mixing the mud - do you get better control with the polymer mud or with the additives? I believe the trowels I have range from 1/2" notch to 1/8" vee. Good tip to test on scrap with different trowels and mud to see how it goes. Also a good tip on feathering/tapering back to the edges. I think I have a similar roller for wallpaper seams. Will have to check.
I'm also a big fan of these
wedge type spacers, but I thought that with the mosaic they wouldn't work. I thought they were for leveling "regular" sixed tiles. They do make amateur work look really good though.