vCenter Appliance 5 vs 5.1?

One of the biggest challenges I find in supporting customers is the constant changes, updates and lack of clear summarized documentation, especially on vCenter appliance.

I am working with a vCenter Appliance 5.0 that is using the local database option. We are at 5 hosts and 42 VMs including desktops and servers. Now, a few questions:

1 - Is there a hard stop at 50 VMs and 5 hosts or is that just the recommended max?

2 - Will going to vCenter Appliance 5.1 gain us anything?

3 - On vCenter 5.0 and 5.1, can you use SQL 2005 or is SQL 2008/2012 required?

Thanks so much in advance!