You state a few goals, one of which is screening for privacy. I think the solutions you are proposing are contrived and lacking in effectiveness, and you're trying to squeeze too much "interest" into the mix, which would ultimately create the opposite effect. It seems to me that you would create a visually stronger artistic statement and more effective screen if you were to vastly simplify the solution. I would also create a faux entrance at the street level so that the arrival experience had some convenience and architectural interest. The floor space there ought to be more like 6' x 8' or 8' x 10'. My drawing has just a simple arbor, but it could be any number of things and even include a waist-height shelf so you have a place to set packages temporarily. This is a place to start brainstorming...

Bamboo is a great choice for containers!! And you do not need to restrict yourself to clumpers - running bamboo is easily contained in large tubs. Boxwood would also work but does grow remarkably slowly and would need to be sheared/trimmed to get the very sharp, clean look you seem to favor. Japanese holly is very similar in appearance and grows somewhat faster so that is a possibility as well, especially the cultivar 'Sky Pencil', which may naturally offer the look you like. Other narrow, columnar needled evergreens with a very restrained habit could work also - Cupressus sempervirens 'Tiny Towers', Cupressus macrocarpa 'Wilma Goldcrest', Juniperus communis 'Compressa', etc. If the phormiums are newly planted, you may very well have some hardiness issues. In the PNW it is not necessarily the cold in winter that knocks them back but rather the combination of cold and our typically winter wet soils. They require excellent drainage and/or a coastal location to really thrive in this area.

Comparatively slow-growing planted features like arborvitae hedges take YEARS to size up - how long are you willing to be "killed" while you wait for this to happen? For instance let's say to get what you are visualizing a planting needs to be 20 ft. tall in at least part of the area involved. If the kind of plant chosen averages 1 ft. per year in height increase on your site you will be waiting 20 YEARS (minus the height of the plants at planting) before the desired level of screening is produced. This was the solution: >Trellises, pergolas, outdoor shades and curtains, and/or shade sails will get you want you want<

Your garden is really wonderful, with all that stonework out back! I garden in Southern Maine, which is the cold part of Zone 5, and have spent 20 years trying to avoid looking at the neighbors. A garden is supposed to provide a sense of enclosure! With afternoon shade, a dogwood should be fine…I have a Korean dogwood, Cornus kousa, which blooms a month later than the native dogwood, Cornus florida. It is also not affected by spot anthracnose, which can plague Cornus florida varietals. There are some unicorn evergreens out there, but they do tend to be pricey. I would suggest a dwarf Korean fir varietal called Silberlocke….it is the tall one in the first picture, and there is a group of three in the second picture. That’s fifteen years of growth that you see. Wisteria on a VERY sturdy arbor could also be beautiful.