How do I register a DBA to sell my pottery if I move overseas?
You might want to set up your LLC while you are still in the US, however since you are leaving Virginia (I presume very soon?) you might want to consider registering in a state like Wyoming. You can then set up the banking and credit card processing in the US for that company, and conduct your business from Ireland.
Since we are not familiar with Irish corporate laws it would be hard for us to give any meaningful advise as far as how to conduct such business legally in Ireland, I would recommend you to contact a local attorney or CPA to discuss this point.
As far as DBA goes, if you already plan to register LLC there is no need to register DBA (just use the name you want your business to use as the name of the LLC).