Are you a solicitor? Is any of this legal advice?

A quantity surveyor reads building contracts for a living, so I will tell you plainly what yours commits you to, what a clause does to your money, and what I would push back on before you sign. That is commercial and contractual opinion, and for most of a build it is what the moment needs. It is not legal advice, and I never pretend otherwise. Where wording itself has to carry legal force - a contract amendment, a dispute heading somewhere formal, the words full and final settlement on a final account - that is a solicitor's ground, and the honest service is to say so at the point you reach it rather than after. The two professions sit comfortably side by side, and a build that needs both is better for having each doing its own job.