The reliable way to hire a tradesperson

it is semi-detached house built in 1920s; solid wall construction. approx 720 sq ft (according to estate agents). There is a lot of space all around the front, back and side of the house. The walls are quite cold, and I think are damp. Insulation is required. what insulation is more suitable/appropriate (rockwool? celatex? any other?) is one better than another? Is there an optimum time of year for it to be installed? (summer?) or does it not matter? presumably it has be dry weather?

My Triton T80 EasyFit electric shower gives too hot water or cold water intermittently within 30 seconds say.

I have just had my new roof fitted. Marley double roman tiles. The joint between my house and next door.the new tiles that have been fitted i think have been cut too short and look like they will fall out.