[gr8fl4porsche]

An estimate is not an estimate.
When the contractor gives you a price - that is the price.
If he will not give you a set price then find someone else.
He has to prove to you when an issue comes up that the additional money he is requesting is not included in the original price.

So,

Draw up a set of approved plans and a contract that clearly states each and every line item that is included in the remodel.
The more clear the contract the easier it is for you and him to get along and get things done.
Go thru every detail of the remodel from the demo to finished area specifying every responsibility and exact model numbers of finishes, applicances, # of coats of paint, type of windows, doors, trim style, etc. Be very clear about the level of quality that is acceptable to you. Monitor the project yourself everyday. I would spend a month going over every single detail and product you want in your house. Do not let the contractor make any decision about products - he does not live there - you do. If additonal work is needed that is not included in the contract - get a price agreed upon prior to commencing the additional work.

Set up a payment and progress schedule, withhold 10% retention until complete, require lien waivers from subs and suppliers.