A Three Pages Long Dream. Too Long?

To answer both questions: It's your novel. Do whatever the heck you want.

If the plot demands that he only meet the love of his life in chapter four, so be it! If a dream demands being written for three+ pages, then go for it.

If it doesn't work when you rewrite/edit, you rewrite/edit those parts until they work.

We can't tell you how to write.

I think that if the dream is interesting enough to hold the reader's attention for three pages, then you can make it three pages. If the reader is sat there wondering what on earth the relevance is, then it might be a good idea to cut it down. And as long as the book is interesting enough and everything you say before the romance is introduced is relevant, then that's fine too. It's kind of hard to judge without reading it, really.