I also buy from the farm store, but it helps to live where there are lots of farmers.

Electrolysis will be the easiest and cheapest way to clean the fasteners. I would find a steel mesh basket to put them in, connect the basket to the charger. Stir them up a time or two to get all the rusty surfaces exposed.

When we reuse fasteners at our museum we paint them. If the're big we brush on two coats of oxide primer, then enamel. For smaller stuff we spray, a minimum of two coats primer and two coats enamel. You also need to keep the paint to a minimum on the threads.

Fred
52 3600
69 C-10