First, check temperature data for your "cool water fish" at
www.fishbase.org. Walleye will eat a YP or BG up to 1/3 of its body length. So your 18" walleye will eat 6" YP or BG.
SMB will eat another fish up to 1/4 of its body length. So a 18" SMB only eats 4.5" YP and BG. Keep in mind that an 18" walleye is about 2lb and an 18" SMB is close to 3.5lb.
Be prepared for your YP population to fluctuate. Adult yellow perch will eat yoy YP, in some lakes YP only have significant year classes every 5 or 6 years.
Also, it is my personal belief that WY can control BG populations, when stocked at the appropriate densities. In one study 2 yr old walleye consumed more grams of BG than 2 yr old LMB, in the same lake. BG are not coaddapeted to survive with WY. WY also have high rates of consumption and have a gape similar to LMB.
Bill already said this but it bears repeating. You may need to run an aerator all summer or year. If the bottom becomes anoxic you will force fish into warmer surface waters, by areating you may increase the temp at the bottom but this will not harm fish as much as low or no DO.
