Having one side of the pond above ground works great, and it gives you a whole different view of the pond than you usually get, because you can get nose to nose with the fish and plants. In a fully in-ground pond you'd be lying on your belly in the plantings to get that view. Also great if it is wide enough to sit on, for viewing or just enjoying a drink in the afternoon. My old pond was built into a steep slope, so it had a 3' retaining wall as one side, and then was cut into the slope for the other three sides. Perfect for resting your elbows and watching the fish.
Regarding numbers of koi, here in the pond forums, I usually see a recommendation of 1000 gallons per fish. One of my pond books says 2" of fish, not including tails, per square foot of surface area. So if your pond is 11'x7' = 77sq ft surface= 154 inches of fish. And you need to plan for fullgrown size, as that 4" koi can get to waaaay bigger than that.
I'd recommend starting with comets and shubunkins for 2 reasons. 1. they are a little cheaper and have lower requirements when you are just getting a pond going; and 2. It is a good way to check your area for racoons, heron, and other fish-eating varmits BEFORE they take off with your foot-long, $100 koi. And, if you have no problems and all looks good, there is no reason you can't add koi in with the originals. They get along fine together.
Looks good!
Jen
keep up the good work.
