I must confess that I have a huge distaste for ivy and vinca. They are both invasive and I think you would regret planting them in the long run. Ivy will overwhelm your trees and shrubs and everything else. Vinca will suppress everything at ground level and spread far and wide. In PA you might consider native ferns, sedges and grasses. Ernst Conservation Seeds (in PA) is where I order a lot of my native seeds and plants from. You might also want to consider redbud trees and serviceberry shrubs and similar smaller scale native trees and shrubs.

Looks like a great project!

And it's almost exactly like my property including the restrictions imposed with a flood retention basin.

I have a few questions though ...

What's growing there now?

You said no terracing, is this being mandated by the conservancy district?

Maybe I missed this, but how big an area are you landscaping?

Is it accessible for maintenance (mulching, weeding, trimming, etc)

You mention a 15' change in elevation but what is the distance that the slope covers (or what is the angle of the slope).

Something you might want to consider is an ornamental fence that runs along the top of the ridge. Nothing tall to block the view of the house, rather something people can lean on and enjoy the view. We had no problem with standing on the edge of our ridge but many people were umcomfortable with that. If nothing else, the fence provides a feeling of security. Ours is actually an extension of the railing of a small lookout deck that extends out over the hill, but I would guess too informal for the design of your house.

Tell us more please!