Like mentioned in title:
Does openHAB 2, in one instance, supports more then one Z-Wave controller / stick for two or more independent ZWave networks ?
If Yes, how to enable this option (edit/add entry in: runtime/bin/setenv ? or set some variable ?)
If I try to add second Z-Stick, I see only one tty already used by first one.
Briefly: It is not possible.
Workaround: mqtt-eventbus and few openHAB instances.
If someone is interested, I will explain more.
It is - the binding will work fine with multiple controllers if you use the development binding.
@chris - I’d like to add a second controller to set up any new and eventually migrate all of my existing devices over to it (UZB to Aeon gen5)
Is it the case of plug in, discover on the serial port and that’s it?
Can both be master?
It’s no problem to have two sticks running, but you will need to include the second one into the network created by the first one if you want them on the same network.
Both can not be master - they will fight for control. The main issue here is that many devices only allow a single node to be configured in ZWavePlus association groups, so it is not possible to have two master controllers in this case. The way the binding works is if you select master on a controller, it will do all it can to ensure that it configures the device to report to itself - if there are two masters, then they will fight 
Is it possible for the master controller zstick to be of 1 freq (eg EU), and the secondary controller zstick to be of another (eg US)?
No, for the same reason that you can’t include devices from a difference region… devices on different frequencies will never hear each other. When you tune your radio to a station, you are receiving that frequency and will not be able to hear all the other stations.
Thanks Scott.
Can you suggest how to setup another z wave network (within the same household) to cater to z wave devices of another freq, and how these 2 networks can link to each other?
I’m sorry, but this would be illegal and discussing it would go against the rules of the forum. I didn’t think of this when I first responded or I wouldn’t have replied, but I am not comfortable discussing it any further.
I’ve trawled the forums but I’m not sure of the answer to the 2 usb sticks scenario I’m thinking of. I want to use 2 sticks each with a separate set of included devices. One stick is actually on a usb extender such that it can serve a second building. I’ve read the other options re 2 openHAB installs, socat etc but I rather prefer a simpler world… So just clarify on Chris’s comment re 2 sticks - can i run 2 sticks on the same instance both as primary but running completely separate z wave networks. I have a pi3 running openhabian. Any experiences or comments would be much appreciated,
Yes
Thanks Scott - the remote location had a Vera controller for Z wave but I have had such hassle with the MiOS binding this seems a much more stable and straightforward way to go.
I will be very interested how you set this dual z stick configuration up. Please share when you get it going .
thank you!
The stick is arriving the weekend - feel free to PM me if I don’t report back in a few days 