The only restrooms I know of on the Parkway south of Asheville are at the Pigah Inn. There's an old stone rustic bathroom just past Graveyard Fields in the Black Balsam parking area, but even a minute inside one of them can be a total assault on the nostrils.

North of Asheville, there are restrooms in the Ranger Station at Craggy Gardens. But they are only open during the season and you might arrive to find them locked.

The trail up from the Craggy Gardens parking lot to the top of the mountain is definitely worth doing. It is quite steep in places, but the plant life surrounding you is awesome. It's not too far of a hike, in spite of the steep upgrade (remember....it's all downhill from the top!). On the peak, you'll find an area with stone walls to sit on and take in a 360 degree view of the mountains. Take a camera.

There are restrooms at Mount Mitchell as well, but they are only unlocked during the season.

Thanks for the info on I26 and I81. There is NO doubt that 81 is nicer. BUT 75 is too far west--honest.
As for the Parkway, at most or many exits you can get off and find a gas station for a rest stop.

Oh my goodness! I've been away from here for a while and I just checked in and WOW! A lot of info is still coming in. Thank you everyone! I copy/paste everything you all write in here. Thanks again so very much!

Need suggestions as to where to stay when we overnight in Wilmington on way to Charleston from OBX. Everything I've looked at so far seems quite pricey as its on the beach. Should we just wing it and look for a place off the hiway?

You can probably wing it, but Wilmington is not very far to go. It is about an 8 hour total drive, I would estimate. If you start early you could get to charleston. My sister drove from Litchfield to OBX pretty easily leaving at 9AM.

Consider staying downtown Wilmington.

Well, since I already have reservations for Charleston I have to overnight on the way SOMEWHERE between OBX and Charleston. It was suggested here earlier that Wilmington was a worth a stop. However searches have not turned up any good suggestions as to where to stay that doesn't break the bank. Anything near a beach is $$$ and for 1 night it's not worth it. I'm open to suggestions...

There will be plenty of chain motels in Wilmington. I imagine if you google for Wilmington visitors bureau or such there will be a big list. You could even try priceline.
However the time you are travelling is getting to be pretty prime time for that part of the coast and might even be the Azalea festival--probably a little late for it, I guess.
It will be about a 4 hour drive to Charleston from there. Nice drive down the coast--CONgested at MB but otherwise just fine. Don't speed below Georgetown.