There are no easy answers to your questions, since multiple factors play into the equation.
In reference to your first question, the amount of money you make is a direct correlation to the effort you put into yourself and your business. If you were to poll professional detailers you will hear pay scales for ~$15000 - to over six figures. Part of your business plan should be goal setting and your target income. That income needs to be realistic and the object is to make it so the business is profitable/rewarding. For some that may be $25000 for others it could be $50000. Money is not the sole motivator for some running their own business and are willing to sacrifice income for flexibility in schedule, family or rewards in self employment. You can make what you want as long as you are willing to work for it. This is not an easy business!
Regarding your second question, the amount charged for detailing. Once again there is no single answer. Price reflects what the market will bare, quality and services offered. Definitions of detailing are vague and not used
with consistensy which only confuses the general public. There are establishments that offer a "detail" that consists of :car wash, vac, windows and a coat of wax while you wait, to be completed in less than an hour for ~$50. On the other hand, a client comes to my store for a detail which requires 4-8hrs of work, appointment and over a hundred steps from a price range of $200 - 600. It is amazing how many people don't realize there are levels of detailing and that this is not a cookie cutter profession. When determining your price levels you need to look at the competition and see what they are offering in terms of service, price and quality. Then a consideration has to be made on the cost of business- i.e. rent, utilities,supplies,equipment,advertising,insurance etc.. Knowing the costs upfront allows you to come up with a budget. Then you can figure out how many cars will it take to cover the expenses, save a little and pay yourself.
I know the answers provided were not concrete, but there are no simple answers. Each owner is unique in his/her contraints,goals and ambitions. One thing I would suggest is use the resources available to you in developing a business. There are typically local organizations, SBA for one, that offer counseling(usually free) in business development. Go to the Chamber,they might be able to assist you. Research is key, don't jump in blind. There is very helpful information here at Detail City.
If you decide to take the plunge, my suggestion to you is : DO NOT try to be lowest priced detailer!! I can't tell you how many guys each year, come to me saying they are going to 'take me down' just based on their cut rate pricing. It won't work no matter how many cars you get if the price can not carry the expenses.
Good luck
Doug