Wilmington is pretty good diving, as is Carolina Beach - right near it. I went out of both this season. We did the City of Houston, the Frying Pan Light Tower, the Cassimir, the Hyde, and 28 mile ledge. All were nice dives and conditions were good.
Seas were pretty snotty in Wilmington..we went out with Aquatic Safaris (about a 30' boat -
http://www.aquaticsafaris.com/) and were in 5-6 foot seas. Our first dive went off ok, but the captain called it during the SI and we got beat up heading back in (the kind of beat up where you have to wear your mask on deck so you can keep your eyes open from the waves washing over the deck and hitting you...lots of puking too).
In Carolina Beach we went out with Seaduced on the SpearIt, which was a 25' six pack with twin 400 HP outboards. That little sucker made about 28 kts and we were on the City of Houston in about an hour and fifteen minutes (that is like 40-50 miles offshore).
As far as the Liberty Ship, I think that was a type of transport boat. I bet they are referring to the Ramsey. I have not been on it, but it is an inshore artificial reef...so it will be good, but not great (isn't any diving good?
).
Good luck! You will have a great time...here's a source for shipwreck info:
http://www.nc-wreckdiving.com/shipwrecks.html