i have startet with a single DN2-HW-APL for testing and setup and it works fine and well no issues, after reinstalling the deliverd node with a new version i usesed 2.3.3.4 as a start over USB Stick
if u have a UPS connected i also dont see any issue to run it a very long time alone , after a few month the other hw appliances arrived and i have added them. In small Installations u dont need any HA only backups and u a are good, For easy setup use Enterprse also as Cluster link , activate LACP für Portchannel and use all Interfaces in 10gig for more bandwith so u need only one uplink Group, i have used 2 one Enterprice link, 1 for Cluster link
The real deal here is, ever interface ip range must be configured same if u later dont use the Internet Interface but u have configured it on the master, u need to do so also on the other nodes, also dont update the master node or u need to wipe the other new nodes and reinsatll them over usb with the same version like 2.3.3.4, also update all the driver in CIMC,
u need 3 identical nodes down to the hardware what i know
NO!!! mix of differnt hw appliances are possible same cpu same ram needed 3 identical twins
