Stay over at least one night in Sopot, they have a campsite there too.
I have just looked at flights again and i can fly from London to Gdansk for £37.77 so i may do it that way and spend a day and night in both Sopot/Hel area and Slupsk then head across to Poznan, Warsaw, Wroclaw then Krakow and fly home from Krakow - is this a bit ambitious for my first visit or do you think its do-able in 8 days, I will be walking most of the way?