Create a business plan. You have to market yourself and find out if you can actually make a living doing this. Prove you have the ability for secure transactions. Obtain liability insurance. Make a name for yourself first, with providers who can recommend your good work. Know the rules/guidance for federal, state, commercial and MA plans, which sometimes vary by state. Are you a pro-fee coder and do you need to know how to code for the facility? What specialties can you code, and does that limit your market? Learn the provider licensure rules state by state (they're not all the same). What software do you plan to use? What's your contingency plan if your system goes down? Can you integrate information with your clients? Will they feel comfortable with your security platform? How will you be paid? You'll need an attorney for client contracts and an accountant to manage your funds. If you're in the US, you will be taxed. If not, a US client may still need to report payments made to a foreign contractor to the IRS, requiring you to complete Form W-8BEN or W-8BEN-E to certify your foreign status and confirm the income isn't subject to US tax. What kind of legal support do you need if you inadvertently code/bill non-compliantly? Are you eligible to work for an organization that takes Federal Money (i.e. are you on the OIG's exclusion list?)
I would answer all of these questions first.