Nice list, but its a bit OTT, your not getting a £100000 handcrafted piece of furnature - your getting a mass produced item placed in your house.
I would go with a simpler option. 1) find several large national pluming companys. 2) get quotes from the cheapest.
Advantages - they will probably be cheaper, each company should have every one trained properly to all required standards (or they risk big fines)
Many of the expenses will be subsidised. Consumables/materials will be bought in bulk
Any rubbish, just take it to your local tip. As a person (and not a company) it *should
iirc* be free and it will be put in the ground exactly the same.