Hi, I get the choice of Arborvitae so there is an evergreen. It is a good one to give a more foundational base. What type is what I am wondering. Low mounded is the one I would use. If Arborvitae is not what you want then Yew or Boxwood would also achieve the intended look. As for a ornamental tree, as long as the bedding space is provided then perhaps a Magnolia or a Crype Mertle? I'm not in your zone so that would be a great question for the nursery you are working with. Check out the neighborhood and look to see what other people are doing with this type of planting. The more mature lawns will speak volumes as they are established. Trust yourself you will see what looks good and what doesn't. As for the sketch, the plan looks good just a little vauge on the seasonal color part. The fact that it is a layered look is nice and I think you will enjoy the affect. One thing I see in the pics is I think there is a Barberry planted by the garden hose, (if I am wrong I'm sorry.) This is thorny and will be difficult to work around. Love the Barberry but would use it as accent or as a skirting planting. Exapmple of this is skirting around upright Junipers, Arborvitae or can be used to skirt a ornimental tree. The design uses an Arborvitae witch makes the area more user friendly. By the way, nice home!