Sounds like quite the endeavor! It was long so I can't speak to many specific parts, but here's a couple things that came to mind...
For your walkie-talking and intercoms and all that, have you looked at SIP? Maybe run a little asterisk or freepbx installation; you could even get an XMPP enabled chat interface as well that might well eliminate your need for IMAP email; if not, there are open source projects such as
http://www.hmailserver.com - that might suit your need.
I like owncloud and will probably do something similar...
For the VPN to your brother, there are plenty of ways; one very simple one is the $99 ubiquiti edgerouter - or if you like the DDWRT route, I'm pretty sure that has something built in... I like the edgerouter because it can be an easy site to site VPN as well as VPN server for remote access and supports all the basic protocols (VPN, LT2P, OpenVPN).