@Herman - keep scaring the tourists- it will make finding spots easier
Where are you staying? Are you intent on U-352 or do you just want some exposure to NC diving? Do you have AOW and/or deep experience? What about open ocean? Like Herman said, it's not like diving in the islands or the keys.
Enough of my questions, now I will try to answer yours
There are much better dives than the U-352 (though good to see at least once) but if you want to do U-352 you want to go out of Beaufort/Morehead City. Olympus, and Discovery run multiple boats. Other boats, off the top of my head, are run by Atlantic Beach, Diver Down, Tortuga. They're all good but I think Discovery and Olympus are more set up for the single diver. Don't ignore the others, you can sometimes get on them if the group booking them wasn't able to fill the boat.
You will end up going to whatever site they decide to go to that day, based on conditions and diver preferences. About the only possibility of doing 4 dives is to add an evening charter to an inshore site such as the Indra. They don't run these every day but you could get lucky. Depending on delays, you could also end up getting back after your Indra charter leaves. That would suck.
I used to dive a 5mm all season. It was overkill in July and August but let me dive comfortably from early May thru mid-November (especially with the addition of a hooded vest).
If you just want to do some good NC diving, then you might also look to find something out of Hatteras or Wilimington/Carolina Beach.