SRM Licensing?

Currently our enviorment looks like this:

• two hosts running 9 vm's
• Equal Logic SAN
• vCenter server 5.1
• vSphere Essentials (expired)
• about 3.5TB of data
• 55 employees

Looking to impliment SRM to a second site. I am planning on do the following:

• upgrade primary site to vShpere Essentials Plus 5.1,
• install a Dell T620, (128GB, 4.2TB RAID 6 local storage) at secondary site

1. If I was to use SRM can I use the license keys from my primary site on the server at my secondary site?
   1. If not, can I purchase vSphere Essentials for the second site?
   2. Or do both sites need Essentials Plus?
2. SRM has some nice features but I am wondering if its overkil for this small enviorment.

Thanks for your help