Hi Friend,
Here is the great post that will give you more insight.
Upgrading to the vCenter Server Appliance 5.5 from Windows vCenter 5.1 — The Lone Sysadmin
On your queries:
VCSA maximum:
Hosts (with embedded vPostgres database) 100
Virtual machines (with embedded vPostgres database) 3000
Hosts (with Oracle database) 1000
Virtual machines (with Oracle database) 10000
Hence, VCSA is capable of handling your workload.
I'm investigating the theory of building a clean VCSA server, disconnect ESXi hosts 1-by-1 from vCentre and simply re-connecting into VCSA. (rebuilding resource groups, etc as part of the process)
Ignoring the reporting/audit history, I'm trying to determine is this an accepted upgrade route?
Answer: As per me, if you are ready to ignore vCenter history, this is the simplest route that you can go for i.e. building clean VCSA and re-connecting hosts into VCSA. Whatever features you enabled from earlier vCenter need to be re-configured. As you said, HA etc. is not enabled, it reduces complexity for sure. You are correct.
On licensing :
I am not good at licensing but as per me it should not be the problem. You can talk with VMware support/sales.
on SAN:
Yes, you can use same LUNs for 5.5 servers as 5.1. However it would be great if you go for VMFS 5. You have option to upgrade VMFS 3 to VMFS 5 easily but I will suggest you to migrate your data to other LUN , delete evacuated VMFS 3 LUN and build VMFS 5 as new. If you upgrade from VMFS 3 to VMFS 5, you may not be in the position to leverage all features that VMFS 5 offer.
Building from scratch would give you all the features. http://www.vmwarearena.com/2013/07/difference-between-vmfs-3-and-vmfs-5.html
Hope this helps you