If you plead guilty to a domestic abuse battery how many years it will be before you will be able to purchase a firearm?

Depends on the state you are in and whether you wish to purchase or carry. Provide the details, engage an attorney and get a firm opinion as to the current status of the law, which will most probably change before you would qualify. The right answer would be to hire an attorney to deal with the domestic violence charge in order to keep it off of your record. What you do today defines your future.

You would have to expunge your record. The wait period after sentencing is state specific. You can find this information online along with the required forms.

Never. Lifetime ban.