If I download Pages / Keynote / Numbers on my MacBook, will I be able to download it to my Mac desktop without buying it again?

Yes, if both machines are using the same iTunes account for purchases.

Yes.

stedman1 wrote:

Yes, if both machines are using the same iTunes account for purchases.

Stedman,

OSX iWork apps are purchased on the Mac App Store, not iTunes 😉

Jerry

You may download any app purchased from the Mac App Store to any of your Macs using the same Apple ID. If you have an iOS device, the iWork apps for iOS are a separate purchase from the iTunes Store.