My Kentucky Blue Blend seems to spread faster when she's a little higher. My opinion is to let her grow a little higher. Helps get those roots nice and strong thus helps her get ready for the summer. +1 on the milorganite. Awesome summer fertilizer. Won't burn the grass, get the benefits of organic and a slow release nitrogen will get her green with a slow growth meaning you won't have to cut it every couple days and she won't burn out like she does after using up all the quick release nitrogens in synthetic fertilizer. Plus, longer helps control nasty summer weeds. Best of luck

As far as grasses go, buffalo grass is a warm season grass that might not be very successful, if at all, in your z5 location. Kentucky blue, especially in a mix, might be a better choice. There is an outfit in East Rochester, Crossman Seeds, that specializes in blends of turf grasses that are especially suited to our climate. Google their website. They have about 9 different blends, one might be right for you. If the perimeter of your property is a mix of sun and shade, privet hedge might not be a good choice. I have a neighbor with exactly the same situation and she has been befuddled trying to get her privet to be full and lush. It just wants full sun really badly and isn't getting enough. In addition to makalu's edible suggestions, which sound quite intriguing, maybe blueberry as a hedge. Yews also tolerate shade pretty well, take a good shearing at any time of the year practically and just keep on coming. They live nearly forever. In front of the windows, I would think maybe of a box hedge, which can be kept nice and low.

I am a zone 8b girl so I have no idea what works up there where you are, but there are some short drought hardy native grasses like buffalo grass, some gramas, curly mesquite grass. What grasses grow in short grass praries in your Zone and area? I did bump into a grass provider from that area of the country. Their name does escape me but I think google might cough them up. No AC... what a dream for me. Me I let the native grow . I have no lawn, just native grasses and whatever moves in..

"Best" is of course highly subjective. A couple of ideas off the top of my head: Geraldton wax flower, Chamlaucium uncinatum Australian tea tree, Leptospermum - several species. Named varieties will tend to be smaller. Carefully research mature height before purchase. I think of these as shrubs, but the "airy" description and ultimate height suit your needs. Both will tolerate dry periods once established. Water weekly after planting for 2 years or until plant is well established. These will do best in full sun. Alternatively, if you prefer something more vertical with a bare trunk and foliage up top, I can recommend specific palms if you describe your climate in greater detail. Coastal, inland, fog, dry, cool winter? What is your garden style?