By all means, buy the Buy Europa Universalis III Chronicles. Not the Complete Edition, that lacks the last 2 addons.
I have my doubts about EU IV. Those individual national ideas could cause more harm than do good imho. And that practically everything depends on monarch power seems also odd. Either in historical context as well as for balancing. Other things as the trade routes for example, seem excellent.
So I expect that EU IV will require some time till it will be great too.