new design to existing windows based infrastructure

Hi

we have following existing infrastructure. we need to redesign it to make it

 *secure

* high availability for databases and applications

* fastest disaster recovery

1. domain controller+DNS+file server windows 2008 r2

2. exchange server 2010

3. Microsoft dynamics database server

4. front end server for Microsoft dynamics 

5. RDS 

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