I would not recommend cloud as you have no guarantee or insurance for availability and safety of service and data.
For authentication Win2008R2 is OK and you can put desktops on domain as well install Exchange with full outlooks on desktops. For network infrastructure like web, dns, dhcp, openvpn, svn, monitoring etc just use plain Centos with webmin.
For large files storage there is openfiler with xfs filesystem. On openfiler you can install apache, webdav etc to access those files.
Use xen if those servers won't have too much load.
Finally opmanager is free and easy monitoring.
Hp dl servers are okay, even supporting remote KVM, but laptops only from dell.
For network switches buy only those which are high performance and relatively cheap. Slow and expensive ciscos are the worst.
Wire everything up properly including ups, management ports etc and you are the master :-)