Every ounce of gold is basically the same as every other ounce. There is no way for a company to create unique value in the gold it produces. And, as such, gold is a commodity that trades based on supply and demand. Physical gold is usually traded in the form of bullion, which is simply a gold bar or coin stamped with the amount of gold it contains and the gold's purity. (Bullion is different than numismatic coins, which are collectibles that often trade based on demand for the specific type of coin and not on their gold content.)    
A. The short answer is 'When you need it.' Gold, first and foremost, is wealth insurance. You cannot approach it the way you approach stock or real estate investments. Timing is not the real issue. The first question you need to ask yourself is whether or not you believe you need to own gold. If you answer that question in the affirmative, there is no point in delaying your actual purchase, or waiting for a more favorable price which may or may not appear. Cost averaging can be a good strategy. The real goal is to diversify so that your overall wealth is not compromised by economic dangers and uncertainties like the kind generated by the 2008 financial crisis, or those now unfolding in Europe and Japan.

This is an obvious simplification of a far more complex history. However, in some ways, it was only natural that early humans would begin using the precious metal as a way to facilitate trade and accumulate and store wealth.  In fact, early paper currencies were generally backed by gold, with every printed bill corresponding to an amount of gold held in a vault somewhere for which it could, technically, be exchanged (this rarely happened). This approach to paper money lasted well into the 20th century. That said, modern currencies are largely fiat currencies, so the link between gold and paper money has long been broken. 

Bullion coins sell for a premium over the market price of the metal on the commodities exchanges.[9] Reasons include their comparative small size and the costs associated with manufacture, storage and distribution. The amount of the premium varies depending on the coin's type and weight and the precious metal. The premium also is affected by prevailing demand.