Answer: I think dichondra would be a waste of time and effort so far north. Crownvetch will withstand traffic but has a somewhat rank growth habit and would look out of place in a residential area. (And yes, it can self seed and be a problem.) If your soil is sandy and well drained, a creeping thyme such as Thymus serpyllum would be a definite possibility, as would the Roman Chamomile (Chamaemelum nobile). Mint on the other hand would not. Mint requires adequate moisture and in fact appreciates a bit of shade.
No matter which plant you settle on, it will have a better chance of success if you work in a generous amount of organic matter when you prepare the soil for planting. You might also consider running a soil test to check both fertility and the pH since some of the herbs, including thyme, prefer a neutral to alkaline soil.
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