That's all there is mammaleigh, there are other 'old wives' methods, but they are just about as accurate as flipping a coin though it is fun to try I suppose.  They are so contradictory though, if they lay flat out they're cockerels, if they lay flat out they're pullets etc etc, fact is, they ALL lay flat out sometimes!! There are other things like that too… most are a bit silly.

I'd love to try to learn to vent sex them, I'm afraid I'd need another human to show me though, that's how I learn best usually.

To feather sex them, you will need to wait till they start to grow their hackle feathers and their saddle and tail feathers, it takes time… but really, what would you do different' if you knew right now?  I can't imagine destroying the cockerels right now even if I knew!   I'd have to feed them all and wait till they're big enough to eat or find new homes for.