Question #1:  Is there a limit to the number of HXII-BP beltpacks on a system as there is for the original HBP-2X beltpack?

Answer:  When using the HXII-BP beltpack as a Digital Power Line beltpack, the 20 beltpack limitation remains the same (10 beltpacks per digital power line, 2 digital power lines per HMS main station).
When using the HXII-BP as a PoE beltpack, more than twenty total beltpacks may be on the system. There is a limit of 60 devices may be connected to a single HelixNet system. 

Question # 2: Is there any data limit that we need to be aware of that would reduce the number of HXII-BP / desktops / HRM-4X remote stations that could be connected via Ethernet?- How about CAT-5 / 6 cabling limits?   Anything that we should be aware of?

Ans:  60 units is about the limit for the Ethernet bandwidth available on the Mainstation (100Mbps). But that number also includes the units on the Powerlines (Beltpacks, Remote and Speaker Stations, 2wire and 4wire modules).

Clear-Com recommends you allow a safety margin and limit the total number to 40 units per mainstation (mix of Ethernet and powerline units)
Any unit connected via Ethernet is subject to the normal 100m rule from device to local Ethernet switch