1) You are going to need a business license, and collect/report sales taxes.
2) You are going to need what ever local zoning you need to do business
3) If operating out of your home, and you have a homeowners association, you are going to have to clear it with them too.
4) Likely the state of MD has something to say about storage of enough ammo to make an ammo selling business viable.
All of the above (and likely more) IF you are to do this commercially. If you are just selling off the stash you already have I don't see that there is an issue.