A) Technically, the amount of gold that exists on earth is finite. So, with a pure gold standard the amount of "money" would be finite. However, using coinage, coins could be made with measured plugs of gold surrounded by less precious metals, thereby making gold coinage practical in size and in value relative to goods. Alloys are not necessary. Using gold plugs to establish the value of coins would mitigate the finite availability of gold.
B) My answer in part A takes care of this question, but suppose a person had pure gold coins. As the supply of goods increased relative to that of gold, prices would fall making products more affordable for the consumer. What's bad about that?
C) Governments should not have the ability to introduce more currency. History has shown that when governments are given the ability to "make" money, they live beyond their means at the detriment to the affected society.
D) Ill-willed monopolies can only exist with the assistance of government. In a free market, producers must meet the demands of consumers. There exists a market price where maximum profits are realized. Above that price, profits fall because people become unwilling to pay it based on the utility provide by the product or service. Below that price, profits fall because the added demand at the cheaper price is not able to make up the difference. Mathematically speaking, there MUST be a market price such as I described. Even if a monopoly is established, it would have to charge market prices in order to maximize profits; there is no way around it. Apple has a monopoly on iPhones. What do you suppose would happen if they charged beyond what the consumers of the market were willing to pay? Regardless of the "rarity" of the product, competition will always exist in any practical scenario. For instance, if oil producers decided to charge $1 million per barrel, biofuels would take over the market very quickly. Only when governments grant special privilege or create barriers to entry can ill-willed monopolies exist.