Mother of Thyme on Lake Superior

I live in Minnesota. Our back yard is on Lake Superior silt and receives direct sun. I am interested in replacing it with mother of thyme which I understand would be hardy. The area does not receive a great deal of traffic and that sporadically and infrequently.
Is my information correct? I am really sick of trying to maintain a lawn and mow, etc.

According to my zone map, the northern half of Minnesota, USA is zone 3 and the southern half, zone 4. None of our thymes will survive a typical zone 3 winter, but English, French, silver, lemon, orange spice, creeping and wild thyme,( also called mother of thyme), will survive zone 4 winters.
However, a bigger problem might be your soil. Depending on how sandy your silt soil is, you might have to do something to improve drainage to have the thyme grow thick enough to make a good lawn. Thymes also do not like drought and in very sandy, poor soil, water retension might be so poor that you have to work in lots of organic matter to cut down on sprinkler use.

How difficult is it to grow from seeds? What is germination/growth period?

Wild thyme is easy to grow from seed. Germination might be slightly improved if the sown seeds get light, so make sure the seeds are surface sown and just pressed in. They should come up in 6 to 26 days. In common with most perennials, growth is slow at the beginning and only really takes off the second year. During all that time you must control weeds. It is therefore suggested that you start the plants in seed flats and transplant to their permanent places the second spring. You could use the time to eradicate all other plants from the future thyme lawn so that the plants have no competition at the start.

What is the spread pattern and how aggressive is it?

The clumps tend to double in size every year, but I have not run across a thyme yet that was hard to contain.

I have gone to native plants and natural landscaping throughout the rest of the yard.

The native plant material will love the environment just as it is and you may have to watch that nothing aggressive invades the thyme lawn.