you are going to need some hand holding.
once you and your future architect/designer come up with a plan you like and can afford, follow their advice when it comes to a builder that can execute it.
they'll have guys they know and trust to pull off the vision. check out everybody's references.
don't think you are going to save a few bucks by supplying materials like windows. your paying the builder to deal with the headaches of scheduling and work flow. no sense adding another dimension to the puzzle, it often only makes things take longer.
lets face it, if you were a pro at this you wouldnt be asking a surf forum for advice.
My buddy did exactly this.
Hired a design/build firm to build an addition. Told the firm just build the addition and he was going to do the finish work like bathrooms-etc. Then hired some cash union guys to build his kitchen while the firm was remodeling.
Firm told him they had to move a pipe in the kitchen. He rents a jackhammer and just starts going at his foundation to move it himself. Busts the pipe and full stop to his project.
As you can guess the firm was pissed at all of this nonsense.
They put him at the lowest priority and the work took well over 1 year when it was supposed to be 1 month. If there was other workers there or he was doing a project they wouldnt come and do the work.
So yea. Dont do that.