I can provide partial answer: there is no native export, except html5 and html5 in wrappers. I saw alpha-test of .exe export here on the forum.
I don't think you can add in-app purchases (for iOS for example).
Try to reach limits of the free version of Construct - 100 of actions per project - there is no other limits. That way you will be sure if you need it or not.
Or better wait another answer, from Rojohound or Ashley or somebody else more reliable than me NugMan2012-06-15 20:12:47