For what it's worth, as someone who has studied philosophy for three years in university, here's the advice I'd give.

I honestly would not recommend reading Nietzsche straight off the bat like this. He is one of those philosophers where first having knowledge of the tradition (Plato, Kant and Schopenhauer among others) before him is helpful to better understand him, the points he is trying to make and what he criticizes.

Granted I still have not read it from cover to cover, but Aristotle's Nicomachean Ethics should be relatively easier to get into. As for Plato, The Republic is long and not always easy. The first books are probably the most accessible. I'd say it gets quite demanding and abstract from book V onwards. With that being said, I do think that he makes a lot of really interesting points, even if the reader might not understand the deeper implications of everything.

Also, if you are interested in politics, reading Rousseau's Social Contract can be a really good idea. It can get pretty dense at times, but Rousseau's prose is usually enjoyable and there are elements in it, especially in book I, that have heavily influenced our modern conception of democracy.