Flash chilling is very simple. Just make sure you have a fairly large ice bath (ice and water that is at least 50% ice) and put the meat immediately from the heated bath into the ice bath. This will rapidly chill the meat prior to refrigeration. Make sure you leave the meat in the ice bath long enough for it to chill to the center if it's a thick cut or a roast.
1 How big should I expect the swings in my home fridge to be with normal usage?
The mild swings from opening and closing your refrigerator door a couple times a day aren't going to really make big difference. Just make sure you don't leave the door open for extended periods of time.
2 If I have a second fridge and the door rarely opens, what will the temperature swings be there?
There are a lot of things that influence the temperature of a refridgerator besides opening and closing the door. A refrigerator goes through cycles for chilling (and for defrosting) etc where the temperature varies. Some brands of refridgerators (i.e. Samsung) have separate cooling systems for the freezer and fridge portions so freezer defrost cycles do not cause swings in temperature in the fridge section.
Also, an empty refrigerator loses a lot more heat than a full refrigerator when the door is open. Storing plastic bottles of water or cans of soda and beer on empty shelves will actually make the temperature more constant over time since they retain more heat (or "cold") than air. Of course, if you turn a fridge into a beer-fridge, chances are that the door is gonna get opened a lot more.
3 Since the botulism concern is due to the vacuum, am I correct in thinking that this concern will disappear if I remove the meat from the vacuum to store it? Obviously, this approach would reintroduce all the normal safety concerns with storing cooked meat.
Sous-vide cooking should pasteurize the meat if it was cooked long enough and kill most . Keeping the pastuerized food that is sealed at a controlled temperature is going to preserve it for much longer than breaking open the seal and allowing any pathogens in before keeping it at the same temperature.
The most important thing is to follow the established safety charts for cooking times, temperatures, using correct flash chilling and then following the safety charts for storage temperatures and duration as well.
Virtually every case of botulism ever recorded in the past 50 years is due to improper home canning. The risk of botulism from a commercial product is so low that you literally have a better chance of being struck by lightning and almost as good a chance as being struck twice in the same year.
There are 145 cases reported in the U.S. each year and 65% of those are infant botulism, 20% from wounds. It's hard to get statistics on infant population, but there are 314 million people in the U.S., so I estimate the chance of getting botulism from food there to be 0.00000692675% in any given year.
You may not live in the U.S., but unless you live in a country with extremely poor or nonexistent safety standards (in which case you have more important things to worry about anyway), I'd advise you to stop worrying. You are about 20 times more likely to die in a fire and 200 times more likely to die in a car accident.
As far as the spores go, they generally aren't dangerous to healthy adults, they affect infants and those with depressed immune systems, hence the heavy proportion of infant botulism cases (often from honey). That's why the WHO warns people not to give honey to infants under 1 year old, but doesn't advise any similar precautions for adults (The reason for no advice for adults is that their stomach is acidic so the bacteria cannot grow and produce the toxin. But infants have lower acidity in their stomach and botulism bacteria from honey can grow there. Honey always has the bacteria. )
Botulism spores can only be killed at extreme temperature, i.e. above 120° C. Boiling water is 100° C, so don't even try to kill them this way. You would need a pressure cooker at very high pressure, and this is why low-acid foods must be pressure-canned; simply boiling is not enough. On the other hand, the botulism toxin is denatured at 80° C, so boiling anything for a reasonable time will make it safe from botulism, but not necessarily from the many other bacteria and/or toxins that can be in spoiled food, such as those produced by certain e.coli strains.
There are plenty of things to worry about with commercial food - salmonella in peanut butter, listeria in lettuce, listeria in spinach... the list goes on and on, but one thing that's generally not on it is botulism, and I think the constant attention here on it actually makes matters worse by taking attention away from other, more common and equally serious issues. Seriously, one person died from contaminated homemade ham and now you're afraid to eat commercial mozzarella cheese?
If you aren't an infant, don't do home canning or home food preservation, and refrigerate your food properly, you're not at risk for botulism. Period. You are, however, at risk of so many other things, and really should try to learn more about food safety in general - from which you'll definitely learn facts such as boiling for 20 minutes won't make spoiled food safe.
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There is absolutely real truth to improper sous vide cooking and botulism. Clostridium botulinum is an anaerobic organism - it grows when there isn't oxygen - like in sous vide vacuums and canned goods.
The risk is that sous vide cooks both without oxygen and at temperatures so close to the perfect repoduction rate for the organism. If you cook it a little lower than recommended, you could be creating a perfect place to reproduce. Clostridium botulinum dies around 126 F (52.222 C) - so most sous vide won't go lower than 130 F (54.444 C).
The opponents state that the temperatures in general are far too low and if we were cooking for a few seconds, it would be. Luckily, pasteurization is a function of temperature and time. This is part of the sous vide magic. Bacterial death is a result of heat and time - if you have a high heat you may only need it for seconds. If you have lower, but sufficient heat, then as long as you cook it long enough (see recommended reading below) - then you can still pasteurize the food. Sous vide often cooks foods for hours and hours - either for taste and/or pasteurization sake.
A great resource for information here is Douglas Baldwin .
Additional, real, danger comes from if you store your finished product in the vacuum bag at improper temperatures (not freezing). Botulism spores need to reach 250 F (121.111 C) to die (this is why, in canning, some food needs to be pressure canned). You won't hit that in sous vide cooking. If you cook the food, cool it, and then store it in a non freezing temp - there's a real risk that the spores could eventually become active and reproduce. If you're going to keep sous vide food after its been cooked, generally freeze it and then reheat (quickly, in sous vide terms) in an eating temp sous vide bath to consume.