rebuilding my existing infrastructure for high availability , fault tolerance

Hi
we have following existing infrastructure. we need to redesign it to make it
*secure
* high availability for databases and applications
* fastest disaster recovery
server 1. domain controller+DNS+file server windows 2008 r2
server 2. exchange server 2010
server 3. Microsoft dynamics database server
server 4. front end server for Microsoft dynamics
server 5. RDS
server 6. application server for GO global, time guardian , payroll, accounting, etc
7. sonic wall acting as gateway and firewall for our 30 remotely connected stores across country.
your help and comments will be appreciated.
Thanks