KenONeill

To make a pre-facelift grill and bumper fit a facelift car, you'd need the pre-facelift front wings, bonnet, headlights and indicators as well. And then have to insure and be able to sell the resultant frankencar.

That could well be the cause of the noise then. The good news is that they are not compulsory: the bad news is that replacing it would require you to remove the stub axle (or perhaps not so bad, since you can cut it away and not need to replace it).

As long as the gloop is of sufficient volume to fill your tyre size, I can see no reason why not. After all, just because the car came with $brand1 tyres ex-works doesn't mean that you can't replace them with $brand2.
 
OTOH you can not re-inflate a torn sidewall with gloop, so maybe it's time to think about buying a wheel and tyre, plus a jack and wheelbrace?

1) Probably; certainly a new cell is the quickest, cheapest and easiest way to check this unless you already own VCDS and a suitable lead.
 
2) It's well documented, but quick summary - Open the pressure bottle and clean the 2 metal prongs with a flat-blade screwdriver. If that doesn't work, a new OEM bottle is under £20 from a dealer.

The basic problem is resonance between pad, disc, and sometimes dust shield. You can sometimes cure it by any of:-
Fitting adhesive-backed pads that actively stick to the pistons. Fitting new "anti-squeal shims" (but only if the specific calipers had them originally). Throughily cleaning the calipers. Applying copper grease to the pad backplates. Changing the make of friction material you use. Removing the dust shields. It's also been observed on drum brakes (most usually on FX4 "London Taxis", by which I mean the original 1960s and 70s vehicles, or on heavy trucks with drum brakes).