Ground Cover for Flagstone Path

I have a rather extensive flagstone walk (190 square feet) which meanders lazily in and out of shady spots. I am looking to fill the spaces in between the stones with a suitable groundcover that is:
1. hardy,
2. relatively trample resistant,
3. would do well in sun or shade (or would consider separate varieties one for shade, one for sun),
4. low growing and mat-like so as to choke out weeds,
5. lastly, something that is fragrant and flowers part of the year would be wonderful.
Is there such a plant that exists for my needs? If so can I get it from seed or plugs and when would be the absolute latest to start from seed? I live in zone 5 on the south shore of Lake Erie, comparable to the agricultural district of Niagara and Niagara-on-the-Lake in Canada.

The sunny portions of your walk are easy: there are several varieties of mat-forming scented thymes that will give all the features you are looking for. For example, our own 'Orange Spice'(TM) thyme will do very well in this situation. You could also try some of the non-fragrant varieties such as 'Minus' and the white- or rose-flowering creeping thyme. Woolly thyme makes a very nice contrast to the darker green creeping thymes. All of these varieties form thick mats that do not exceed 3 cm in height. None are available in seed form, but they come in plug trays.
If you are willing to allow plants to grow a little higher, you can try the only seed-propagated creeping thyme available: wild thyme. By far, starting wild thyme from seeds is much less expensive than planting plugs. Naturally, it takes longer to establish a thick mat from seeds. Because thyme seeds are so small, and because wild thyme takes about a year for a seeded patch to fill in, there is more chance of failure, and more work is required to keep the weeds down until the patch is established.
For the shaded portions of your walk, the answer is less clear. There are no hardy, shade-tolerant herbs that are low, mat-forming, and suitable for the crevices of a flagstone walk. The thymes will tolerate the semi-shady portions, but those that are permanently shaded will require something else. If you don't mind mowing the walk every once in a while, you could try yarrow (Achillea millifolium). This herb can produce a very nice green mat, but it will get tall in shade unless it is mowed periodically. You may find, however, that there are other low perennials not normally considered herbs that are better suited for you. An example is Sagina subulata which looks all the world like a true moss (which it isn't), but we do not carry it.