Chances are you could already be in violation of BATF rules.
Have you;
1. Held someones firearm overnight at your location/possession of someones firearm while they are not present.
2. Performed a service on that firearm.
3. Charged said person money, for your profit.
If you did all 3 of these you must have an FFL.
Doesn't mater if the gun is shipped in, or handed to you. If you posses it, work on it, and charge for profit, you are required to have an FFL as a Dealer/gunsmith.
As far as getting an FFL it is pretty simple. Call BATF, and ask for the application packet. They frown upon at home business unless you have a building separate from your residence for business purposes. Contact your city or township, if you are zoned, and get permission in writing before you apply.(you will have to sub-mitt this with your application) You will be required to have the head law enforcement official for your jurisdiction finger print you and sign off on your application. (finger print cards come with the app. and are returned with the app.)
If you want insurance to cover this business, well that's a whole nother can of worms.
I would suggest that you form an LLC to protect you family assets.
The application will ask if you have conducted this business already. If I was you I would say No. AND DELETE YOUR POST NOW.
Good luck
Jim