I am mainly concerned about the first dock section just sitting unconstrained on some paving stones.
Are you concerned because you want some movement, or you want zero movement?
You could dig a post hole near the end of the dock and fill it with concrete and set an eyebolt. Run a cable to an eyebolt in your last piece of deck wood and put a turnbuckle under the dock connecting the cable. You could then tension your "hold down" to whatever you desired, and easily change the tension at a later date if you decide your prior tautness was not optimal.
