To your edit:
An easy way but probably not the best is to just stop mowing it. If you currently have a weed free, chemically enhanced lawn this might take a while. If it is your average lawn that just gets mowed, you probably already have native grasses and plants there. Clover, violet, dandelion, wood sorrel and many others are commonly growing in lawns unless treated as "weeds" and sprayed.

The best way to do it would be to dig up or rototill the entire area and prep it as a flower bed. The existing ground cover would most likely out compete the seeds sprinkled in the area, so removing it is important.

Thats good to hear, Broad Mountain Mint is one that I am looking to plant this year.

Most natives don't require much care, this is their home environment so not much to it as long as they get the required sun. The amount of sun will dictate what seed to get. I'd say any of the asters, bee balms, golden rods, cone flowers and Joe pye weed would be easy enough.

I ordered seeds from Wild Seed Project in October. Most need a cold stratification period but im sure there are some still available. Weston Nursery also has native plants available in the spring and there is lots of good info available on Native Plant Trust web site

I live in southeastern MA and have only seen rats in Boston, Worcester and Providence and the surrounding areas but mice are everywhere. Mice are fairly easy to control though.

I've never heard of a license to harvest green crabs, they are invasive. Take as many as you want