Hello and welcome
You do sound out of your depth [that's coming from a confident DIYer]!
My advice would be to find a friendly spark who will let you help with the donkey work. Digging the trench for the cable, maybe attaching accessories to walls, even clearing up and making tea. Doing some of the labour will save you a few quid [many of our members not too keen on digging trenches] and you'll learn something.
Do you know a local spark? Where in Lancs are you? A number of our members are in your part of the world.