The big question is, what type of content are you trying to access remotely? steaming video? Just documents?
Video streaming would require a media center that does transcoding. For document access, that should be relatively simple once you have a VPN connection since you'll be virtually on your home network.
For simplicity, a VPN router would replace your Apple Airport Extreme 5th Gen Wifi router as it needs to be externally facing(connected to your cable modem). You can have the VPN gateway inside your network but configuration get trickier that way.