I think you may be right. Your "lead buttons" are probably pewter. All your finds definitely look period. Usually the pewter buttons will have a design, insignia or letters on their face. Hard to tell from the pics but some of your balls look like .750 brown bess balls. You have some research to do I'm afraid. Button back marks and the type of shank attachment will help date them. Probably have to clean them up a little. Your buckles look period and with the age of your coins could very well be rev. When I get home I'll see if I can post a couple reference guides for such items.
It's very unusual to find all those items in one area. Many of us that have collected rev artifacts don't have that many buttons after literally years of searching. Especially pewter buttons.
Fantastic bunch of relics. As I said, the only way to know is serious research. Not only on the items themselves but what could have occurred there at the time. A camp, a landing, a skirmish etc.
Anyone that collects the elusive rev artifacts would kill for a stash like that. Shame about the condition of the coins but that's pretty typical. As I said, I'll see if I can post some reference info when I can. Unbelievable!