It looks like a Franke Eiger but you would normally see the Franke logo on the base at the front. If no luck, you could try packing out the existing O rings. Carefully remove the rings, put a couple of turns of PTFE in the groove and then replace the o rings. Smear with silicon grease and...
If its a mains cold water pipe, you can T into it to feed the washing machine. Will it affect hot water supply from the combi boiler? Probably but only occasionally and briefly if the the washing machine fills when someone is using hot water but this will likely be the case wherever the washing...
The basin mate seal kit from screwfix should give you a good seal but will need the backnut to be considerably more than hand tight. If you can't get tools onto it, it won't work. Can you move the pedestal? I usually loosen the basin securing screws and get a shoulder under the basin. Hopefully...
When in the dispenser, the bottle would be upside down so the bottom becomes the top so the hole is cut at TDC which then becomes BDC when used as a tank. Stop typing, put the laptop down, have another beer.
Yes. It should be fitted above the normal water level so would be dry until a fault occurred. It would then transfer water to the overflow pipe. This water would not be under pressure. The seals and connections are unlikely to cope with constant submersion and/or higher pressure.
DP showed you...
If the joists span the whole width as shown and you are wanting to cut notches for pipes, then there are building regulations about where the notches can go and how deep they can be. The middle of a span is not acceptable.
Does the second stopcock just isolate the boiler or the whole house. If its just the boiler, it may be worth having it there so the boiler can be worked on whilst keeping water supply to toilets etc.
You may need to adjust the position of the bolts to take into account the thickness of boarding and tiles. If you have locked them by putting nuts on the back, this may not be possible. Follow the manufacturers instructions.
Sadly, the ones you have found are not likely to be better quality and they will eventually leak as well.
I try to avoid the ones where the shaft is held by a circlip. If there is a gland nut, you can at least, have ago at repacking the gland to stop the leak.
If the valve is regularly turned...
If you have low pressure hot and cold at the bath taps (tank in loft, hot water cylinder, no pump) then the pressure/flow from a bath/shower mixer will be poor.