Brake Disc Thickness

sounds like you didn't have the opportunity to bed them in before getting them wet. Google to find tips on how to do that. Essentially you need to get them hot, the jury is out if long hard grabs work best or short sharp bursts. The pad needs to glaze and particles of the pad need to get into the disc (or something like that). It's not unusual for pads to last a single ride in the wet. Get metal sintered or metal for the winter. www.superstarcomponants.com

No idea about the minimum and you'll probably not find anything on that, especially anything official. Greg?

I've run some discs for about 5 years without the width looking like an issue. I've actually just bought some digital calipers so perhaps I could take a look and compare them with my brand new ones...

the pot - assuming that it is stuck out a little (?) i suggest opening the reservoir at the top to make it easier to push back. You may need to bleed them if they are stuck as air and contaminants may well have got into the system depending on how far out they are and for how long. I'd take them to a shop if you are new to this and don't have the right bleed kit (warranty?). Otherwise a rag (clean) to clean the external part of the piston so it moves freely. Don't be tempted to poke them with anything or they won't move freely as the surface won't be smooth anymore (wish I'd thought of that before i did once....)

If they're stuck in then i'd get the bike in a stand, remove the wheel and pump the brakes to get the pistons out but use something to hold the free one in (and prevent the stuck one from coming out too far when it does move). If it comes out to far it may fall out and drop oil everywhere (you'll need to bleed them then!)

hope this helps

Not unusual to go through a set of pads this time of year, especially if they aren't the sintered ones.   I think all pad manufactures recommend 'bedding in' pads, as Mark suggests. 

No idea about the minimum either, though I have a recollection of reading a couple of mm's before changing (the width of a fag packet?).  I normally get to a point and decided to change them, especially if I'm going on a long ride or it's going to be particularly muddy, rather than wait till it's bare metal on metal.  If the pads I've removed have any life left in them, then I'll carry these as a spare set, just in case.

I've never had the misfortune of a sticky calliper, so I can't suggest anything specific.

try some fenwicks or muck off disc brake cleaner that might work on the sticky calliper

or any motor bike disc brake cleaner as they seem to be alot cheaper

Thanks for the advice chaps - Mark, just for interest could you measure your caliper? I also have a set of digital calipers, so we can compare notes!
Caliper sorted itself out with some manipulation, and just bought some of those Allstar/Superstar pads - currently running Shimano scintered pads on the rear and Swissstops on the front. Both are lasting well.  The Shimanos don't squeak - the Swissies do. Pad wear slightly less on the Shimano though it is at the back.
Just as a footnote -
Sometime shortly after this post, I fell off after washing-out and couldn't walk for 2 weeks, nearly busting my hip in the process - there's still a lump, however I've been back on the bike a few weeks now!