I bought the material for my 67 300 from SMS in Oregon. Last year the price was $79 yd for the factory pearl white vinyl. The seat foam had to be made by hand by the upholsterer. There are no pre made covers or foam available for this model.
The guy I used charged $900 to make new seat covers...
Since you are on Long Island, try Don's East Coast Restorations in Lindenhurst. He is the one that keeps getting recommended to me from the locals. I have not personally had any work done there.
I had the same problem with a late 90's Riviera. I rolled down the window and sprayed WD40 on the door linkages from the lock assembly area to the area of the interior latch. Continue to work the linkage as you spray.This did the trick for me.
I would go with the white interior, black dash, to me nothing is as classy as a white interior.
I wouldn't worry about the difficulty of keeping it clean, unless this is your daily driver.