I think you should study psychology, then specialize in the particular period in the history of psychology that interests you. When you reach your master, you will get a historian of psychology to supervise you. These people are normally employed at the psychology departments, not at the history departments, which concern themselves mostly with traditional history, wwII or elizabethan england etc.
Also it will be very difficult for you to evaluate psychological ideas without having some psychological foundation. There is normally a history course included in a psychology degree.
Why do i know this? Well, I am not a psychologist, but I was asked to study the history of psychology. I was interested in the transition between darwinism and functional psychology in the late nineteenth century. I was then told that they actually have few students who are intersted in the historical side of psychology. If you, for instance, decided to look at Erich Fromm or Franz Fannon, popular social psychologists from the mid twentieth century etc, you willl get some of what you want. The gist of what i am saying is that if you wish to study the history of psychology, the best road is through the psychology departments.
When you say "the application of the history of psychology", do you mean its dissimenation through books and academic culture? You will find both freud and jung alive and kicking in literary studies, but they are basically not clinically relevant. You will find lacan in linguistics, along with many other new ones? One interesting thing is that you will also find some of this in computer programming. At youtube they use psychologists to design their interfaces, i have heard? The "like"-button and "network-theory" made zuckerberg a billionaire. And what is the difference between "a facebook like" and an academic citation and the "H-index"? If you disregard the prestige, not much.
And then you have all the fancy "organizational psychologists" who have been milking business leaders for easy cash for many many decades. (these guys are loaded, i tell you) And then you have the feminist psychologists, Luce Irigaray etc. In sport, psychologist are applied to "motivate" people (often the same sort of people as in business).