Does anyone know what flowers would work best in my space?

I would take a picture of the area you want to plant and go to the local nursery., possibly with a soil sample as well. They are the professionals in your particular area as to what plants do best in your conditions. Usually they will also guarantee the plants as well. To just look up your 'hardiness zone' is not enouugh as it will not take into consideration which trees may be dropping stuff into the soil, morning or afternoon sun, water conditions, and the other particular conditions of your spot.

Here is a good resource for you,however your soil should be amended before planting. https://www.gardenia.net/category/plant/hardiness-zone/hardiness-zone-5/

A lot depends on how much time and money you are willing to give to the project. Both of the above comments are great. Making raised beds is an option but probably the most expensive (i.e. lumber to build the beds and soil to fill them). Container gardening is also an option. Many possibilities.

You can plant some black eyed susans, they're so cheerful!