Does this line sound stupid or wrong or what?!

"Although i realise university, like any other stage of life, will probably not be plain sailing, I am looking forward to finally being able to live the dream I have had for so many years, and to studying my favourite subject to such a high level."

(It's the first half of the last paragraph of my PS)

"Although i realise university, like any other stage of life, will probably not be plain sailing

I wouldn't put this line in, personally. It could be perceived negatively i.e. as an admission of weakness. The comment also sounds a bit cliched, although I guess it can be difficult to avoid this on a PS.

Instead, I would try and sell yourself in a more upbeat way, 'I will relish the challenge', 'I am prepared to work hard to achieve an end product' - kind of a way.