I used to use it as my firewall as well but I've been on OPNsense for a little while now. Lot more bang for the buck in terms of effort vs. out of the box features.

After you've set up your share on the server, map a drive to it in My Computer. Now right-click My Documents and go to properties. Click the move button, point it to the mapped drive, and click Ok. You'll be prompted whether or not you want to move existing files to the new location, say yes.

Once the move is finished, you're ready to set up synchronization. Right-click on My Documents again and click Synchronize. In the lower right hand corner of the window you'll see a button marked Setup, click that. Now check the boxes next to "When I log on to my computer" and "When I log off of my computer" and click ok.

I do this at work and it has worked flawlessly for me thus far. Good luck.