The six month issue is a UCCJEA issue, that is to say a custody issue. If you moved in April, the six months are likely over or just about over; the issue being that if you attempt to initiate proceedings before the six months are up, your ex- can try to reopen the Maine custody proceedings and argue that issues affecting custody belong in that state. He can try that afterward, but after six months the new state would normally be regarded as the children's new home state and thus the appropriate forum for litigation.

You can read the Virginia adoption statutes here - as you can see, they're not impossible to follow but there's a lot to parse. It would be much easier if your ex- would consent to the adoption. As he will not, there is potential for him to argue against step-parent adoption once he's properly served with notice of the proceedings.