===== How many LUN per VSCSI ? =====

It depends to the queue_depth.
Rules per VSCSI: 
<cli prompt='#'>
Maximum disks per adapter = ( 512 – 2 ) / ( 3 + queue depth )
</cli>

If you keep the default queue_depth to 3, the you can map a maximum of 85 LUN per VSCSI or pair if you use dual VIOS.\\
For example if you change the default queue_depth to 20, the you can map a maximum of 23 LUN per VSCSI or pair if you use dual VIOS.
<cli prompt='$'>
$ chdev -l hdisk0 -a queue_depth=20 -P
$ chdev -l vscsi0 -a vscsi_path_to=30 -P
$ chdev -l vscsi0 -a vscsi_err_recov=fast_fail -P
</cli>
http://www-03.ibm.com/support/techdocs/atsmastr.nsf/WebIndex/TD105745

http://capacityreports.com/VIO/vio_tips.html

https://www.ibm.com/docs/en/power9?topic=channel-npiv-multiple-queue-support