Yes, you can run multiple Apex units if you like. Here are some tips:
1. Be sure to change the Hostname on your current Apex before connecting the new Apex to your network. The default hostname is "apex" which allows you to access its local dashboard at
http://apex.local. However, if they both have the same name only one will respond. After changing the hostname you must reboot the Apex for the change to take effect.
2. Do not connect an AquaBus cable from the new Apex to any of your existing modules while they're still connected to the old Apex. Apex units cannot be connected together with AquaBus.
3. You will be able to access both Apex units in Fusion, but only one at a time. You cannot have a "shared" dashboard with tiles from both units.