Best to plant in the spring, either from mail order, or GC if you're lucky, good chance for next year. If you have the space you can grow them in a row with support, like raspberries, if they are purely for picking.

http://www.hallsofheddon.co.uk/chrysanthemums

I would go for sprays. I would also give them a ring first for a bit of advice as to varieties. They are very helpful.

I would agree with Scrumpy sprays are less labour intensive.

You should get most of what you need to know here;

http://www.thegardenersalmanac.co.uk/Data/Chrysanthemum/Chrysanthemum.htm

Thanks everyone, especially for the Websites which I will follow up.