a four-way came with your setup... nice.
the two secondaries you found on the link look like a good deal.
you carbonate wheat beers generally to a higher pressure than other styles, but I have had wheat and non-wheat on tap at the same time and thought each was perfectly carbonated: see you carb the wheat to say, 3.25 volumes, and the pale ale to say, 2.5 volumes, but as long as your distributor has check valves, which most do, you can serve both beers at the same pressure, about 10psi, and there will no problem, just give the wheat one a quick blast at 30psi occassionally if you notice it losing carb.
I know what you mean about the Perlicks being expensive. Standard taps will get stuck (badly) unless used almost daily. I had just one Perlick for a long time and then a picnic tap on the tower as well as for the summer cooler. I've just recently ordered the other two Perlicks.
The amount of volume of beer in the shank is so miniscule that its length makes no difference for cooling.
When drilling into the fridge, the idiot-proof way is go through the door so as to avoid coolant lines. Use a standard bit for a pilot hole, and then a hole saw bit after.
the shanks I have used are 3inch, 2inch, 1.5inch, and 4.8inch, they serve only to connect the beer tap securely to the beer line.
I can show you my setup, are you in Fredericton?, there is no need to spend money on cooling the shank unless you want a glycol tower, which is totally superfluous. I have a very simple dorm-fridge with a wooden collar. I drilled a hole about 2inches wide in the top of the collar and mounted a square tower made of a 1by4 pine board. The tower is sealed, and the beer stays pretty cold up to the tap, but the tap is room temp. Even if I serve as little as 3oz, the beer in the glass is cold.
There is a mathematical relationship between hose length, diameter, pressure and temperature, you can google keg co2 balancing, but the idiot-proof way is about 10-15 feet of the hose I mentioned earlier. Also, the math relationship is not perfect, so it needs to be taken with a grain of salt.
I used to use the polyethelene tubing: not as good, I replaced all of it.