Questions about vCSHB 6.5.1 (LAN vs. WAN and Physical vs. Virtual secondary server)

Hi,

I have a few questions regarding vCSHB 6.5.1:

1) There are two sets of installation guides: one for physical secondary server and one for virtual secondary server.

    What are the major differences between those two scenarios?

2) For vCSHB, there are two deployment options: LAN and WAN

    2a) Which option is more common?

    2b) If one option (e.g. LAN) works in an environment, can I assume the other would work as well?
         And how different are those two options?

3) Is vCSHB backward compatible? Does vCSHB 6.5.1 work in a environment where a previous release (e.g. vCSHB 6.4) works?

4) Which vCSHB release (e.g. vCSHB 6.5 or 6.4 or 6.3) is commonly deployed nowadays?

Thanks.