If you are building a bed on top of the concrete slab (as opposed to having the slab broken-up and removed so the planting is put into the ground), then the information on our Soil to Fill Raised Beds page may be useful. If you are amending in-ground soil, then compost and some good-quality topsoil should suffice to reduce compaction and aid drainage. Extension doesn't collect information about sources of supplies (soil, mulch, etc.), nor do we recommend particular businesses, so we can't say where to purchase, other than that most garden centers and some hardware stores should have sufficient options.

Be aware that Tulip Poplar matures into a very large shade tree (and grows pretty quickly), so will soon outgrow a container and potentially cast too much shade on sun-loving perennials for them to keep blooming. Some of the species you listed will be fine in semi-shade, but a couple (Butterfly Milkweed and Joe-Pye Weed at least) need lots of direct summer sun to thrive and flower well.

You don't need to custom-adjust the soil pH (not that it would be easy to do so where it will remain unchanged after intervening) to meet the needs of particular plants, as long as the soil pH isn't strongly acidic (unlikely) or too alkaline. It's always best to choose plants that suit the existing site conditions rather than trying to change the conditions (like soil characteristics) to meet the needs/preferences of certain plants. Most plants have a pretty broad range of soil pH they will tolerate. You can have a laboratory soil test performed if you want to learn its pH, nutrient content, and organic matter level. The same test will not give accurate results for compost, which needs to be measured with a test specific to organic matter. More information about soil testing can be found on the linked page. Stores selling bulk topsoil and compost should have a soil test report available for you to look at so you don't have to get it tested yourself.

Miri