Your plant choices are excellent and will look very attractive. Mulching under the tree now to depth of 2-4 inches would be a good start. The mulch will conserve moisture and break down into compost. It is very good for your tree. The plants you have chosen don’t need rich soil so compost and mulch should be all you need. Insert the plants into the soil and try to disturb the roots as little as possible. You won’t want to more than 4 inches at one time because doing so smothers tree roots. 
you could add big leaf aster and wild geraniums your plant list but there are so many wonderful hosta in all kinds of sizes, colors and textures they could be ll you need. 

On 06/02/2021 5:41 AM Ask Extension <<personal data hidden>> wrote:

 

 

Your plant choices won’t need extra nitrogen. I like to use a slow release fertilizer. It won’t burn the plants. 

On 06/03/2021 7:28 AM Ask Extension <<personal data hidden>> wrote:

 

 

Thanks you too.