Is your contractor really a contractor? You can check with the Contractors State License Board in California. They will also list results of official judgements against the contractor - but not judgements in process.
If the contractor provides references, call them. If there are several crews, see if the crew doing your work is the same as the one that did theirs. If the contractor points to his projects, visit the people to confirm that they really were done by that contractor.
Contractors are legally required to notify you that you have three business days to cancel. You can waive this right in an emergency, but they should still tell you.
The initial down payment is also limited, depending on the type of work being done (swimming pool contractors can take a larger deposit).
Finally, there are regulations concerning subcontractors and liens - you can read more about this on the State License Board's web site since it's fairly complicated.
Contractors are required to give you a written bid with a price for installing everything listed in their bid, or "per plan". Make sure that they include all the features you want in their bid. Sometimes things get left out, either accidentally or because that contractor doesn't feel qualified to complete that portion of the work.
Material and labor costs fluctuate, due to energy costs, government regulations, type of material and a number of other factors. For this reason, the only way to get a sure price is to get bids. The only way to get consistent bids so you can compare contractors is to have a complete set of drawings so they all thoroughly understand what they're going to build.
Be very careful when making changes. Although some changes can reduce cost - such as eliminating a structure - many don't. Frequent changes can quickly escalate costs - this is why you drew plans in the first place, so that changes would be minmal. A few changes are normal for each project, and typically these are related to site conditions, plant or material availability or another factor. These don't usually have a major impact on the budget, and sometimes reduce costs.
You're also somewhat at the mercy of the project the contractor is doing before yours. If there are a lot of changes going on there, your start date might get pushed back. A good contractor will keep you informed.
Be careful - some contractors have work crews that rotate through a number of projects, so they can "start" right away. Insist on an estimated finish date. If you're really serious about the completion date, you can demand liquidated damages for any work not completed within the promised date. Be sure to set a reasonable time, especially if you're going to ask for liquidated damages, or nobody will bid the project.
It's definitely worth the wait for a good contractor. They will assign a work crew to your project that will work only on your project until its done. So, despite a longer wait to start, you'll normally have less actual time from start to finish.
Most contractors got into their profession because they love to build things and see them take shape. They like solving problems on site - and yes, there will be problems or at least unforeseen difficulties.
No plan can handle everything, especially when installation involves digging. The best process is to work together to find solutions that maintain the integrity of the design being installed. Discuss things in a friendly manner. It will keep everything much smoother and likely result in a better final outcome.