I am one of the developers on staff, so i will try to answer your questions as best I can.
I would suggest that you spend some time looking through the wiki, and looking at our demo video.
This system is far more than a media center, it's a smart home system. As such, you need to build at least two systems...one being your core, which will run all the system services, and media directors that attach to each TV.
LinuxMCE, unlike most other systems, can control your AV gear, and do so with varying devices from web pads, to cell phones, to ordinary remotes, all simultaneously, and all in synch. The media directors and core need to stay on, they currently do not suspend in any fashion, but we are looking for people to add this functionality in....
We have a comprehensive event system which bolts on top of our messaging system, which will do what you ask.
As far as file system, we suggest letting installing LinuxMCE on a small disk, (120GB or so), and setting aside a set of disks to be set up with LinuxMCE's RAID system.
We use Asterisk and FreePBX for the phone system, so you're covered there...
We do require that the core system be your firewallni and gateway and dhcp.. it's where all our plug and play power comes from. Please do not circumvent this.
I suggest doing further reading, but, you'll quickly find that this system, if you follow our recommendations, outclasses everything else that the free software community has to offer, and rivaling and besting systems from vendors like Crestron, Control4, AMX, etc.