I think there are 18 in total- but there is a 'branch' in the campaign towards the end so you may not get to fly all missions
I would suggest you
might want to look at the redone version of the RAF campaign
http://airwarfare.com/sow/index.php/...d-raf-campaign
I know you said you like to finish what you started, but it does fix some of the 'irritations' with the original. If nothing else I would recommend it as a first user made campaign