If you want to get rid of the grass, it isn't really necessary to physically remove it, that's a lot of work. You can effectively smother it out with a thick layer of newspaper or cardboard and a thick layer of mulch (those shredded leaves and branches) over the top. (Do a search for lasagna methods of soil preparation for more info.) Then your understory will be ready to plant with wildflowers, small shrubs, etc if you want a woodland garden, or not if you just want mulch. Besides the decaying grass under that newpaper/mulch layer adds great nutrients to the soil. And if a bit of grass does pop up here and there, it is easily pulled out.

Sandy

It's hard for me to do the math in my mind and picture how thickly your trees and shrubs will be, but from my experience, it will be easiest to maintain if you put down newspapers, several sheets thick and then a few inches of mulch over that to keep the weeds down. If you call around, you might be able to find free mulch. I got a huge load delivered free to my house from a tree service company. It's not as nice as the stuff you buy but the price was right and I got it in the winter so it was free of leaves which makes it break down more slowly. Or your city may have a recycling facility with free or cheap mulch. I agree with Mosswitch. I'd put it right over the grass instead of trying to dig it all up.
I'm not familiar with Maryland's climate but you may need to water them the first year or two when it's dry.

I am quite jealous that you got all those for free! Wow! Sounds like you're going to have lots of berries/seeds for song birds. Spicebush is a host plant for Spicebush Swallowtail butterflies and Sweetbay Magnolia is a host plant for Tiger Swallowtails. Nice bonus.

Cut the grass down as low as possible and then mulch as recommended above. Or rent a sod stripper but that might expose weed seeds. Consider deer protection for your new babies.

If the new plants are very small, as the free trees or trees bought from local conservation sources usually are, you will also need to protect versus rodentia and rabbits. I've lost more young woody plants to late winter chewing and bark stripping by various rodentia and rabbits than to deer.

FataMorgana

Even if you don't have the time/energy/mulch to do the entire area, it will still help tremendously to smother the grass immediately surrounding each plant. That allows you to identify them and also allows the light to reach them. Deer and other potential nibblers also seem to recognize a neatly cleared area as a convenient meal, so I agree that protection will prevent disappointment. Chicken wire and trunk wrap can help a lot.

Martha

Thanks for the replies! I'm going to use a chipper to chip some branches and leaves to mulch at least around all the plants and maybe some of the grass as well. I found out all the plants were sprayed with deer repellent but I also put 3 tree guards around 4 of the dogwoods. I'll use some chicken wire to protect the rest.

Happy Thanksgiving!
TJ