Does this come with the blades, also will fit the Stihl FS40?

I am so sorry, this one is not suitable for your machine and there is no alternative for the 7-3 head which is suitable. You can only get the replacement blades for the head that is recommended for your machine - https://www.lsengineers.co.uk/replacement-blades-pack-of-12-stihl-part-no-4111-007-1001.html