Hi Christera,
Welcome to TFL. First off, let me say that I am relatively new. Also any advice you get here, you should understand that it is not professional legal advice, so don't take everything as gospel.
Your best bet would be to talk to your local gun shop. They will be up to date on all the specific gun laws that apply in your situation. Secondly, look it up on the NRA website (see my link). Thirdly, your local and state government web sites can help, but they are harder to interpret sometimes.
As far as I know the only requirement to sell your gun is that you can't sell to someone under 21. You as a private seller would not be required to do a background check, however you cannot sell to someone whom you know is not allowed to possess it.
To purchase a gun for home defense there is no special licensing requirement as I understand it. If you plan Concealed Carry in public then you would require a license.
Here is where I got my info:
http://nraila.org/statelawpdfs/OHSL.pdf