Food

Are we in "season"? is there a season?

Yes, you need to purge them as they're dirrrty
I've read that they are more active from March to September/October when it's a bit warmer. But I've also read that it's less of an issue in the South of England.

I've also heard conflicting stories about purification. Some people go straight from the river to the pot and others leave them in a bucket/the bath.

I've been told they will cut through nets if you try to keep them for too long but a plastic dustbin with small holes drilled (to allow for water circulation) in a pond etc works well.

None of the above is based on experience, unfortunately.

As an aside, if you want to eat crayfish for environmental reasons then you need to make sure you are taking out the smaller ones as well as the monsters. The larger crayfish will prey on the smaller ones which helps to keep the population in check (a female can lay 300-500 eggs a year, IIRC) so if you remove the bigger ones then you just create "space" for the smaller ones to expand into.

This PDF is quite interesting as it illustrates the issue they pose simply by their sheer numbers.