Hi buddy, VPN links are flakey at best, I wouldn't really advise it, I do this kind of thing a lot (for a living). Dropbox and live drive, also sky drive are best options.
I will use drop box as an example, a 100 gig account, think of it as permission levels, if you have 2 user groups, managers and users, you create 2 accounts, one for each, in the managers account you create a folder called users and add all the shared data, another folder called managers and copy the managers documents to that folder. Next you install Dropbox on all computers that need it a log the people in with the security permissions they require.(user/manager). The limiting factor is speed of your Internet. This comes in to play if you are using VPN or Dropbox though. The issue you have is when more than one person needs to use the same document... Key to this is google apps or share point.
Be open to the suggestions to ensure you get the right solution, from what you have said it looks like your mind is already made up though?