Yes, we have built our own house 4x and remodeled and put an addition on our current home. My DH and I run a plumbing business, all we do are new homes, very little service work. Because of this, we personally knew all the contractors we hired. What was shocking then was to be ripped off by people my hubby works with! Very touchy situation maintaining a working relationship and standing firm on what we thought was fair. ALWAYS ask how much the TOTAL will be and get them to give you a written bid. I can't stress this enough. Ask if there is ANYTHING that is not included in the price. We would get a bid to fill in the basement with gravel and then get another bill for spreading the gravel! So I always ask if this includes everything necessary for completing the job. In our trade, for instance, our bid will be for the plumbing in the house. We do not include the price of sewer and water lines to the house because it is impossible to know how long those lines will be. We always let the builder know that this will be billed separate and give them the rate per hour and cost per foot for the material as a good faith estimate. It's unfortunate how many contractors target people like you who are not "builders" as a way of making easy extra money. That said, you will save a lot over hiring a builder.
Contact your local building/plumbing and electrical inspectors and ask about the contractors you plan to hire. Call them everytime you question whether the work is being done correctly. Look everything over everyday that work has been done. Have your contractors give you a definite start/end date. Do not pay them anything up front. No contractor should require that. We also do not pay until their work has been inspected by the proper authority. Some contractors around here will work a little and ask if they can get a little bit of the money, then they take off to another job and do the same thing there. Ask for references and do call the references.
Good luck!