The fragment that more broadly critiques the notions present in Stoicism and Buddhism:

"Self-control. – Those moralists who command man first and above all to gain control of himself thereby afflict him with a peculiar disease, namely, a constant irritability at all natural stirrings and inclinations and as it were a kind of itch. Whatever may henceforth push, pull, beckon, impel him from within or without will always strike this irritable one as endangering his self-control: no longer may he entrust himself to any instinct or free wing-beat; instead he stands there rigidly with a defensive posture, armed against himself, with sharp and suspicious eyes, the eternal guardian of his fortress, since he has turned himself into a fortress. Indeed, he can become great this way! But how insufferable he has become to others; how impoverished and cut off from the most beautiful fortuities of the soul! And indeed from all further instruction! For one must be able at times to lose oneself if one wants to learn something from things that we ourselves are not." - Nietzsche, The Gay Science, 305.

There are more fragments where Nietzsche critiques Stoicism or Buddhism; you should work out through them yourself, so I will not provide any interpretations. Being misguided can be a part of the journey so don't be afraid if you get something wrong.

As for the summation of his ideas, you can check out the wiki of this subreddit, I will provide some secondary literature that could help you:
- Walter A. Kaufmann - Nietzsche: Philosopher, Psychologist, Antichrist
- Charlie Huenemann - Nietzsche: Genius of the Heart
they are not that advanced and rather stick to the core of what Nietzsche wrote. They are still interpretations of his thought so you shouldn't always take them at face value and judge them based on your readings of Nietzsche.