I suspect you may have created a poor-man's slow-cooking environment in there. You had meat, and liquid, and a median temperature of around 200° F, and you probably also got the bird close to "done" during the first broil, before you even left the house. This is obviously easier to do when the meat is covered (was it in a covered roasting pan?) due to the steam, but the oven does provide some insulation to begin with.
Technically when slow-cooking you should theoretically be able to speed up the process by quickly bringing the meat up to just below doneness/moisture-loss temperature (130° F) and then switching to a moisture-preserving slow-cook method like braising. I think that's what you accidentally did, but it's hard to say for because nobody was there for an hour and it sounds like you didn't check the temperature before the second round in the oven.
My guess is that the second roast at 400° F was probably unnecessary, and that the bird was already done, having been cooked in a very slow roast.
I'm pretty sure it wasn't the basting that helped. It seems to be regarded as a myth these days that basting keeps the meat moist, because the baste really doesn't penetrate the skin (and it's not the skin you're worried about). Basting is done to add flavour, not preserve moisture.
The recipe itself also doesn't strike me as anything special in terms of keeping the bird moist, aside from having a relatively short cooking time (as with any grilling/broiling) and letting the meat rest afterward, neither of which really apply in your case. It was probably the slow heat that did it.
I suspect that the biggest problem here is that your brine isn't anywhere close to being strong enough. Cooks Illustrated has a good guide to the entire process but in a nutshell:
Sea salt is expensive and inefficient for brining; the impurities actually make it more difficult to dissolve and disperse properly. Kosher salt is generally recommended, although table salt is also fine.
A typical brine is 1/4 cup table salt and 1/2 cup sugar per quart, which translates to about 70 g and 140 g respectively per L. For very high-heat methods (grilling/broiling), you halve the amounts. Also, for kosher salt you need to double the volume (no change if measuring by weight). Even the lower, high-heat cooking concentration is almost twice as concentrated as what you're doing.
You also need to scale the amount of brine with the weight of the bird itself. The rule of thumb is 1 quart or L per pound (2.2 kg) of meat. For a whole chicken, which is generally around 6 or 7 pounds, 1.5 L of brine is nowhere near enough, especially if you're brining in a pot as opposed to a bag (does your 1.5 L even cover the chicken?).
It doesn't really matter if you butcher the chicken first (although most people don't). You're exposing slightly more surface area that way but not really enough to matter.
Make sure you are actually dissolving all the crystals! From what you're describing, you're getting high concentrations of salt in some areas and none in others. That means you didn't get proper dispersion. You really need to make sure that all of the salt (and sugar, if you're using any) is completely dissolved, otherwise you don't have a "brine", you have water with a bunch of little piles of salt. Some people will suggest heating or even boiling your brine to ensure proper dissolution; just make sure you let it cool off afterward if you do this, before submerging the bird.
In answer to your specific questions:
The container should be well-sealed to prevent evaporation, not to mention off-odours in your fridge. However, I've used pots with loose-fitting lids and had no problems. It doesn't make a huge difference as far as the efficacy of the brine.
Fridge temperature is ideal. Do not even think about using room-temperature water, that is highly unsafe for storing raw meat for 6-8 hours at a time.
As long as you don't overcrowd the vessel and do disperse the crystals properly, the actual amount of space is not a major issue. If it's exposed, it's exposed.
Longer than 12 hours is not recommended. Actually, according to CI, longer than 8 hours is not recommended. Don't overdo it - you're brining, not marinating.
No matter how you cook any piece of meat, it will give up a certain amount of water and therefore a certain amount of salt (from the brine). Left unstated is why you would even consider boiling a brined chicken; brining is primarily a technique for dry-heat cooking (roasting/grilling), and if you want to boil/poach/braise/whatever then you should be focusing more on flavouring the cooking liquid than the meat itself. I wouldn't bother brining if you're making chicken soup, there are better ways to flavour that.
Best Answer
Why not make your own cheese sauce. You could do something like;
roux, milk and cheese
.Or you could always use something like
ricotta cheese or boursin cheese
that is a spreadable and more natural cheese.