Just a comment from a quilter who considered a long arm.
1. make sure you enjoy the process and have no physical impediment to doing a lot of work on the machine. A good friend tried for a year to do stand up work and her back could not stand it. She now has a sit down machine and is in heaven.
2. source your accessories and additional items like batting, backing and thread. There will probably be inventory. Decide ahead of time what batting and backing you will work with and how much work/time you will do with and without pay to resolve customer issues. You will be surprised what they will expect of you. Inventory takes room.
3. understand the business and sales tax items applicable to your state.
4. please be honest with customers about your ability. I appreciated one long arm quilter who was upfront on what she was comfortable doing. Note: I do not yet do feathers etc.
5. Consider doing as many charity tops as you can to learn how to use the machine and resolve issues before you start doing for money.
6. Have a written contract ahead of time and make sure all costs are explained with a written document that you can hand to a customer before doing any work. So many problems are due to misunderstandings. Know how to explain to a customer that you cannot do her quilt for the .......reasons.