Also consider a development fee. I charge a $250 development fee that is non refundable but is deducted off the final price. This is so I don't sit around for an entire day designing something only to have the person decide that they want a wood gate instead.
Personally, I always take money in installments. X amount up front, x midway and x upon completion. This will guarantee that you have money coming in regularly so when you hit that light switch you'll have power. This is especially useful for things like quarterlies, insurance payments etc. This can also allow you the option of taking a check every week as opposed to the feast or famine method. I've done both and getting a weekly is better for paying bills. No waiting. Plus, if July and Sept. are busy but Aug. is dead you'd get the completion payments for and July and some up front money for September and you won't starve during the month of August, for example.
To finish or not to finish.... ha ha. I have the equipment but the thought of acetone, xylol, naphtha, lacquer thinner, corrosive patinas, and other mind altering vapors makes me sweat. Charge extra for this type of thing.
Be prepared to educate clients. Most people don't realize that metals are a publicly traded commodity and are expensive. Metal is ubiquitous so people think it's cheap. When they balk at a figure it helps if you explain the nature of the business to them.
That's just my .02
Best of luck.