[moneydance] Cross platform, sharing data files, license, family plan?

[dancingbrook]

I have a son in college, physics/computer science major and we are  
using Macs with OSX, Linux and Windoze (rarely). We are hoping to use  
MD, as Mint and Quicken don't cut it.

Questions:
Any concerns re sharing data cross platform?
Any significant differences between platforms in the app itself?
Can I place the data file on my iDaisk and share it with my son there?
Do I need two licenses or can he be like my "spouse" seeing how she  
isn't going to use it?
Are family plans available (as in iLife and Omni)?

Thanks for answers to any of this.