Go to a small, local garden center and have them help you design deep garden beds for foundation shurbs that work in your zone. Consider planting a well designed "island" to look down on and enjoy--again with shrubs, perhaps trees, grasses, and perennials with room for a garden bench with stepping stones leading from house to the bench.

Whole Home Garden Design and Installation; large trees, flowers, shrubs in beds · More Info

Lawncare · More Info

you'va got a nice expansive back yard.

I would replace all the big windows with patio doors that would connect the house to a big deck along the back of the house. Terrace down to the ground for grand outdoor living.

of course, you could do it all in stages.

Build a big Deck first, to enjoy, then add the doors as budget allows.

May be some kind of decking?

I like this one

https://www.finedecks.com/

or with pergola

Adding a deck (maybe partially covered) is a great first step. You could make the deck even more usable by adding a dining area and cooking space. There aretons of options and styles available for designing your deck. Considering how large it could be as well as the slope you’ll definitely want to work with an experienced landscape company to ensure you are getting high-quality materials and installation. Think about making it water-tight so under the deck is usable. Adding different levels with just a few steps helps define space and makes the deck more aesthetically pleasing. Think about adding a fire pit or wall or custom planter pots in areas instead of railing.