I'd opt for #6 shot...and decoys work. If those crows are hanging the same spot daily then they're apt to have a roosting area nearby. That's always a good spot in the afternoons.

If you want a great attractant cripple a crow and let him draw the other birds in. They will try to help him out. I don't know if that's considered legal or not but it works.

Since crows are considered a migratory bird (which is why you have the particular days legal to hunt them and there's a season) I don't know if lead shot is legal but that's all I've ever used and I shoot heavy loads.

Ya dont really have to have decoys , just pick up the dead ones and hang em in the tops of saplins. Heavy load 6's or 4's aint needed either, 7.5's or 8's are fine for crows. All ya need is a good call and try to make every shot count, dont just shoot empty at every crow or they'll just leave and won't come back. Try not to set up in mature timber or the crows will be to high, scrub timber or fence rows work better.