You should have got a heating engineer not a plumber, who could have done the wiring as well.
The valve is normally cold when not in use, but that will depend on how long since the system was last fired up, could take hours.
The pipe to the pump and after the pump would normally be hot if...
If you supply an email in your profile and you are an RGI, I will send you one, if your inbox will accept it.
Otherwise you can get one here http://www.a2zboilermanuals.co.uk
Twenty litres per minute flow for the unvented, the combi should not reduce the mains pressure, may need to have a new mains supply or at leasted checked by water board.
Add an unvented cylinder for your hot water needs, have the combi just feeding the kitchen taps, the extra rads will not be a problem for the boiler you have.
Its more a case of if you want the system or not, the pumps are generally timed for the periods of bathing or hot water usage, the system can include towel rails and the pumps are temperature controlled as well as timed.