Fuel consumption and questions

That depends a lot on the size of the boat

http://en.wikipedia.org/wiki/Beam_(nautical)

That will depend on what type of engine it is, how it's maintained and operated, it should at least be able top charge it's own start battery

That will depend on how often you can get out to sail, learning the fundamentals doesn't take long refining those can take the rest of your life.

Everyone has to start somewhere

Your welcome and welcome to YF.

Assuming you are talking about a small boat around 10m, you'll probably drink more than the engine will.

It doesn't take but a few days to learn how to sail well enough to enjoy an outing. Learning all the other stuff can take years.

By all means take a course now. It will teach you how to be safe on the water and will answer thousands of questions you haven't even thought to ask yet. It will also help you decide what kind of boat you want, or if you really want one at all, and it will teach you what to see when you look at a boat.

Our large boat has a 120ish gallon tank for fuel. The smaller boats carry 40 or 50 gallons. This can vary based on the boat, purpose, etc. The large boat, we keep it full. The small (racing) boat, we keep as empty as possible.

Beam = the width of the boat. Google "Nautical Terms" and you'll get a more technical definition from one of many online dictionaries.

Very reliable. Both of ours have Yanmar engines. Never had an issue with either. Yes, they can be used to charge batteries, or on larger sail boats you'll have a genset (generator) for additional power when / if needed. (AC, etc.)

I can teach you to sail in an hour. It will take you the rest of your life to master it. If you get involved in sailing, sail weekly, or a couple times a month, expect to be proficient in a couple years. All of this depends on you and how much you apply yourself. Could you be a weekend / lake sailor in a few months and enjoy yourself? Of course.

Yes, there's no reason not to take courses now, and or involve yourself in the sailing / yachting community. Take courses, read, join your local yacht club, show up with good deck shoes, a bag of sandwiches, a bottle of rum, and a good attitude, and most importantly, a willingness to learn, and you'll be sailing with the best of them.

Welcome to the forum, and welcome to the sailing and yachting community. I hope you hate money, because you're going to burn a lot of it in yachting!

Cheers-