After been shopping around for ID in the past 2 mths and got scammed by Max's Image for a expensive preview -.-". I guess prolly I've seen the worst and the best (Peter Tay, but he onli does high end & modern design project).
I personally would prefer IDs that are separate from contractors even though its nt that easy to find on the market now. That means they do charge you design and coordination fee in a separate quote (under the ID company names), and the contractor you have chosen from them will bill you separately. But pls beware of some films may use this technique to scam as well because sometimes invoices cant be trust either.
My concern to you is if you squeeze too much on the price for films that does design and build, they may subsidize the material that use during the reno. For example, plywood comes in different grades, they can prolly go for something cheaper or even worse, they may use wooden chip boards (Ikea use it) to make ur furniture in their carpenter workshop and lay a finishing on top of it, its very hard to notice the difference for me though.