The IIIC (Big C) is distinguished by a large viewfinder that has framelines for the 35mm, 50mm and 80mm lenses.
If there is just one set of framelines, then it's a IIIc (small C). Excellent camera, excellent lens.
I haven't looked at prices for these for years. IIIC used to go for about $225, while the IIIc went for about $165.
Leather cases generally have no value. The auxiliary lenses probably are worth about $25 each.
Filter rings, etc., are worth a few dollars unless they're original Kodak Retina-branded items with cases.
Moth-eaten items -- well, I was trying to think of something humorous. Obviously, no value. In fact, I would toss anything moth-eaten.
Good luck. This can be an excellent camera.
A photo taken with a Retina IIIc (small c):