Water/glycol fermentation chiller questions

I'm working on putting together a brewing setup, but have run into something of an impasse with keeping things cool for fermentation. The basic setup I'm thinking of is a mini-fridge with 3-5 gallons of water/glycol mix that gets recirculated through a stainless coil in the fermentation vessel. There are a few questions I have, and I was hoping some of you could point me in the right direction on them.

Thing One: Is that enough coolant for keeping two or three five gallon batches down to lagering temps if the ambient temperature is between 75-80 degrees? (The fermenters would be insulated, of course)

Thing B: How should I size the coil in the fermenter? I'm thinking about using 1/4" OD stainless tubing, good size or too small? How about length, would it need to be 20' or longer?

Thing the Last: What about the pump? I was looking at getting one of the pond pumps, but I don't know what size. In looking I think people were using one pump with controlled valves when they were cooling multiple fermenters, is this correct?

Thanks for any help. I'm sure I'll have more questions before all of this is over.

I had plans to do this in a corny keg, but one with 4 top ports (aka stainless pressure vessel...they ain't cheap though). May still some day.

I'm not sure there is really a benefit of doing this inside or outside of the vessel, if it's metal (and you're going to insulate it anyways). Better sanitize well if it's inside cause it's not like you can boil it. Also, I'd think the thermal mass of the liquid would be behind what the coils are putting out. You may get ice crystals on the coil before your temp probe reacts. Maybe that's not such a bad thing since that may help drop out yeast. It might be a reason not to use glycol though, so it's not too much below freezing temp.

I was thinking of getting one of those 'jockey box' coils cause they are thin gauge and more tightly wound.

I probably will never do this because of the sanitizing thing.

less of a hassle i think would be to get a bigger fridge off of craigslist and just put the fermenters inside. This would hold the temperatures more stable as well.
using coolant you're going to have a problem with overshoot in your temp control system, since the coolant is going to be at a lower temp than your target temp. the beer will also cool unevenly, getting real cold right next to the coils but staying warm in other regions. If you go this route, I would think that putting coils outside the fermenter vessel (but still inside your insulation) would allow the tank walls to even out your cooling.
commercial breweries general use a single glycol pump, but it works kinda like a power steering pump, where it is controlled to maintain line pressure that is released by the valves. How are you controlling the valves? Are you just going to "tune" them by hand and have the pump run constantly, or are they going to be triggered by individual thermostats in your fermenters? you have to account for the situtation where your controls close all the valves and the pump is still running. This might not be an issue, but if you're pump just keeps pushing against a closed valve, it could burn out. Also, the coolant would be more effective if you had a coil inside the fridge as well. Imagine the fermenters soaking up heat, then you're pumping that heat into the fridge, the fridge is then pumping it out into the room again. You need good heat transfer from the glycol to the air inside the fridge in order to maintin consistent cooling. Perhaps you could find a small car radiator that fits inside the fridge. That would be pretty awesome. Otherwise, I would just have the returning glycol run through a coil exposed to the air inside the fridge, before being dumped into the reservoir.
But still, I recommend getting a bigger fridge to make your life simpler, unless you're really good at building systems like this, which I'm not.

my 3 gallon glycol system works in 90F weather, holding the fermentation water bath at about 64F. However, it did NOT work at 1 nor 2 gallons. Lagering will probably require 5 or more.

My system is controlled by my Love controller - it turns on the pond pump immersed in my glycol. (Glycol is stored in my kegerator at 35F and pumped over on demand).
A smaller pond pump is immersed in the water bath and runs continuously, to assure water temps remain consistent all around the tank. The gylcol pumps thru a transmission oil cooler device immersed in the water bath.

in winter, I just substitute an aquarium heater for the glycol pump and change 'direction' of temperature switch.