if i start using iCloud for windows, then upgrade to iCloud drive does anything already syncing change?

Hi, I want to use iCloud for Windows to sync my mac and pc and iPod for bookmarks, contacts, email. My question is: I am currently on Mountain Lion and so would be using iCloud. If I upgrade later to Yosemite, will it cause difficulties or changes with the stuff already being synced? Or will it stay the same, and just add the option of using iCloud drive.

The reason I've not upgraded to Yosemite is that I'm running a 2008 MBP so it is getting fairly old, and I don't quite know about the Photos App yet. Also, I don't need to use iCloud to move documents, so iCloud drive is of little use to me.

OSX 10.8.5

2.8 GHZ Intel Core 2 Duo

4 GB Ram

PC running Windows 7

iPod Touch on latest iOS 8