I'm not using one main builder. I'm managing the trades myself, or using a kit company. Does any of this apply?

What changes is the shape of the work. With one builder there is one contract and one account. Running trades yourself there are many smaller ones, more payments to check, and the coordination gaps between trades are yours to own. Kit companies ask for large payments before anything stands on your site, which deserves its own kind of checking before the money leaves. Tell me how your build is run and everything after is fitted to your answer.