You might want to think about using landscape fabric or another alternative~~weeds are inevitable. I'm also doing a flagstone pathway, and my landscaper recommended it. I have never heard about not using 10" or less pieces because of 'flipping up', but if they're 'buried' deep enough I wouldn't imagine there could be a problem.

As far as the red thyme, it's most likely the weeds would take over before the thyme.

I'm sure you'll get some better answers than what I might be giving. ;o)

The flagstone walk I built four years ago has many pieces that are 3"x4" or even smaller. They have not flipped or shifted at all. HOWEVER, I did use polymeric sand in between the stones, so that helps keep them in place. What are you going to use between yours, to plant the thyme in?

I agree with Patty Cakes that weeds would do as well as if not better than the thyme, unless you plant a lot of thyme immediately. Even so, it could be a maintenance nightmare. How much to you like weeding?

Thanks for the responses! We tried out some different approaches with the stones, etc. and I'm hoping we have settled on using a larger (1/2" - 3/4") gravel that we had leftover from another project. It blends in better with the neighboring mulch than the d.g. I think it also holds the flagstones in better. When we get the whole thing laid, I'll post a photo (however, don't hold your breath - it's taken us a year just to get to this point!)