Answer: You have asked an interesting question. What would work best for you would depend on the local market -- meaning your potential customers -- and on how much of an investment you are prepared to make. Since you want to try this as a money making venture, I would suggest you consult with your local county extension. They should be able to help you do some preliminary market analysis and have up to date information on suitable crops and marketing schemes.
In my experience, it just does not work well to try to grow woody plants such as trees and shrubs indoors. Many of them need the seasonal temperature changes to grow normally (some require a chill before they will germinate, too) and the light indoors is not strong enough to keep them healthy. It is better to have a nursery bed (or containers with specialty soil mix and watering equipment and a sheltered place to overwinter them) outside where they can be grown for a period of years and of course, that requires an investment in time and the space to grow them.
If you want to try something on a very small scale with a minimal start up cost, you might look at some of the specialty houseplants such as African violets. These can be propagated easily and tend to sell well on an informal basis, and grow quite well indoors under average home conditions. Larger scale production can often be accomplished in a basement or spare room under lights. The African Violet Society web site offers helpful information on how to grow these, in case you are interested here is the link.
But again, you will need to try to figure out if there is a good local market for your product before you start growing. Good luck with your project!
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