Definitely don't be worried too much about the size and amount of the books to begin with. If you end up with enough material to make it this way, then fair enough, however writing one amazing book with 5 distinct "parts" within it, would get across your element of having significant sections between each sword being found, yet would relieve a lot of the burden that planning for an ambitious series can give.
I say this because I myself envisioned a trilogy for my first set of books, yet as several posters have said here, there is no point extending parts to boredom or adding extravagantly long descriptions to things if it upsets the pace of the story.
My point being, write however you feel best, whether you plan a beginning and an end, with the 5 swords in the midst (I'm guessing there's a reason they need the swords and that at the end of the whole story there will be some kind of conclusion), or just go blind until the book finds its own end.
If you end up with a modest amount of material, bind it as one book with 5 parts inside. If you end up with an insane amount, separate them into individual books.