Multiple Asterisk

Ok so I would like to know a few things

  1. can you run multiple asterisk and keep all users and sip synced
  2. load balancing if one asterisk starts using two much CPU or proccessors can it automaticlly direct the user to the 2nd asterisk server
  3. domain have one domain like and still register on the nearest or most free asterisk?

I ask these questions because I have a product I plan on launching which requires multiple servers

  1. DNS subdomains to point to servers around to our other servers i.e. USA / UK / AUS
  2. if AUS is full go to our second AUS server etc.
  3. if a person from AUS travels to US It makes sence to connect them to the US server and not the AUS servers.