iCloud with Multi-Boot Drive, 10.8/10.9/10.10

I want to set up a multi-boot drive allowing the options of starting up in Mountain Lion, Mavericks or Yosemite. However, given the changes that have taken place in Yosemite with regards to the way iCloud functions & stores files as well as syncing changes that have been forced upon many 3rd party apps, I'm concerned about rendering either the 10.8/.9 drives or the 10.10 drive as being only semi-functional. What are my options, if any, for retaining as much full functionality & cross-device/platform synchronicity while having active drives running 10.8-10.10? Thank you.