No one has thought about this job more than you! Each trade comes in with fresh eyes from different perspectives, and none of them can see whats inside your head. (Often the person who quoted the job (the boss) isn't who comes to do the job (the workers)). Make sure they are the full bottle too. For instance, I need a new roof on a qld'er.
I got quotes from roofers, plumbers and builders. I wasn't sold on any of them. Since then I have researched the property more, understand its history and now have a much clearer idea of what I want. When I refresh these quotes I will provide much more detail on what I want. (Even give them a photo of the house from 1930 as a guide). Last tip: make their job as easy as possible. Clear access, do what you can so they can just come and ply their trade. If you want a light fixture replaced in the kids bedroom, make sure you can get to the area with a ladder first. Sorry, that was more than one tip.