Can these be used for buckshot loads like 00 or #1 or #4?

Yes but you'll only fit eight 00 buck pellets which just under an ounce. I have many of these for clays and decided to load some defense rounds. You can squeeze a ninth but the crimp starts to bulge. I've also put 1 Oz of #4 buck and get I think 20 in there, which is an 1 ounce.

Can these be used for steel shot

i wouldn't. steel shot is harder on the barrel and there are other wads specifically made to protect the barrel like this - https://www.ballisticproducts.com/TPS-12ga-2-3_4-preslit-wad-for-non-toxic-shot/productinfo/3227701/

Will they shoot 1 oz slugs

I only shoot up to 00 buck. I've never tried slugs as my shotgun is a full choke model and the manufacturer doesn't recommend slugs. Sorry I couldn't answer your question. Sam