What is average? What is your fixed cost? What is your variable cost? Do you have any idea the types or amounts of fertilizer to use? Do you have any customers? Do you have any experience? Do you have GL insurance yet?
Some of your questions are impossible to answer without more info. Some of your questions can be learned by spending time reading on this site. The beginner questions are in volumes here. You must apply yourself to reading. There is enough here to keep you up all night for weeks.