It sounds like your options are pretty limited. Fast growing trees are going to get really big. Most fast growing trees also end up being weak-wooded and short lived. 'Green Giant' thujas grow quickly and have far few problems than Leyland cypresses (which I would definitely NOT recommend), but the Green Giants are going to get pretty large eventually (and very possibly much larger than you'd want). You may want to consider a vine-covered fence or even a hardy type of bamboo with a root barrier.

The bars are there because the program you are watching is not wide screen. If you get rid of the bars the picture will be distorted(streched sideways) to fill the screen.

Yes, the wall is north-facing, and the area of the garden within 4 feet of it, where we'd like to place screening plants, is in shade with no direct sun for about 4 to 5 months of the year. I guess we don't understand whether this would be considered part shade, with only ambient light available, or full shade.

Using fertilizer at full strength for epiphytic plants is a no-no. Not only are you wasting $, you are not thinking of how the plant would get it's nutrients in the wild. Epiphytes use aerial roots to climb from the forest floor to the canopy via trees, limestone outcrops, etc.. Some even root directly from seed in the canopy of a tree. Many epiphytes eventually forego their terrestrial roots in the wilds of the Asian/Indian rainforests, where there are yearly monsoons that flood the forest floors. Instead, they use their aerial roots to obtain any nutrients they need to aid in photosynthesis. These nutrients come from canopy detrius, such as broken down leaf litter, animal/bird scat (poop), fungi, lichens, and moss. The nutrients, themselves, are very dilute (there is not gonna be a ton of scat or leaf litter on a single tree- exceptions would be in Eastern Indonesia/PNG/Eastern AU , if a male Birdzof-Paradise has chosen a specific tree to do his mating dance on). Throughout the early morning, when humidity is at it's highest, creating rainforest clouds, humidity and light rain "wash" the litter/scat/etc. down the tree trunk, onto the aerial roots. Any excess natural fertilizer is quickly washed away by the same process. In other words, Hoyas just don't need a ton of food. No plant in a pot does. You run the risk of irreparable damage to the roots via fertilizer burn, and over-feeding can cause an imbalance in nutrients. Some nutrients are harder for a plant to get rid of, creating an unhealthy excess. This excess can inhibit the uptake of other nutrients that the plant can quickly rid itself of, but are vital to the health of the plant. Like water soluble nutrients versus fat soluble nutrients in humans. Most of us can quickly rid ourselves of an accidental excess of water soluble nutrients by drinking a LOT of water. But if we were to ingest an excess of a fat soluble nutrient, well, you'd be hard pressed to find someone who'd down a can of Crisco to rid themselves of the excess.