Under sink disaster area!

[John sankus]

Hi all. We have recently moved into a place and I want to rearrange the kitchen a little, which includes replacing the worktop and the sink, and the kitchen cabinet the sink sits on however, I am a little puzzled by the pipework here.
I've attached a pic that shows the arrangement of the pipes as I can see them inside the cabinet. They all come out of the bottom of the cabinet and carry on, unchanged, through the floor 15cm below.

There are two waste outlets that both go down the same drain - one is for the sink and the other is currently used for dishwasher, although I see no reason why I shouldn't remove one waste pipe completely and just use the one - it looks like I could take the top off dishwasher waste (4) and turn the sink waste 180° and have that going down the same hole..
I have no idea why there are two mains inlets. The mains shut-off tap that sits on the blue plastic pipe (1) shuts off everything, so I am not sure what the other pipe (2) is for. The hot and cold inlets (3) will remain unused. I was going to cut them off just above floor level and put double ended service valves on them, turn them off and leave them under the cabinet so they would still be usable if I needed them.
I would like to have most of the pipework behind the cabinet, so it cannot be seen, although I would have to retain the mains shut-off tap.
I'm not much cop at soldering or joining copper pipes so most of it would be cutting pipes just above floor level and using John Guest speedfit stuff to redirect the pipes behind the cabinet with a couple of angled connectors.

I suppose the question is, is this doable? Is it a stupid idea? (Why is there another pipe (2) attached to the mains inlet (1)?
Any advice would be greatly appreciated, thank you

 

[denso13]

No reason why you can't tidy it all up as you see fit, sinks tend to get a bit messy over the years as things get added and removed.

If the mains going up only supplies the dishwasher and sink then 2 will be feeding the rest of the house. You could cap it off and see what, if anything, doesn't work.

 

[John sankus]

No reason why you can't tidy it all up as you see fit, sinks tend to get a bit messy over the years as things get added and removed.

If the mains going up only supplies the dishwasher and sink then 2 will be feeding the rest of the house. You could cap it off and see what, if anything, doesn't work.

That's the thing - despite that mains shut off tap looking as if it only services the sink, turning it off also cuts off the water to the bathrooms as well...

 

[denso13]

it off also cuts off the water to the bathrooms as well...

Which is probably the other spur going through the bottom the unit.

 

[John sankus]

Which is probably the other spur going through the bottom the unit.

I think you're right... The spur goes down as well as up and that is what services the bathrooms and heating.