I saw in one of the config files or forums that stratux can allocate (I think) 10 IP addresses via DHCP. I have had a phone, a tablet, and the 740 connected simultaneously with no issues. My SkyRadar supports multiple clients, as did my previous SkyRadar. So it should be no issue.
HOWEVER - my tablet drops connection with the stratus occasionally, but it also drops with other routers so I believe its a tablet issue. I have Googled for the firewall settings as you describe, but my tablet doesn't have a "Firewall" option under Security like The Google describes. How old is your tablet? All the firewall hits I've seen are old, so I'm wondering if the setting has been removed from the current Android releases. Or perhaps you're running a firewall app or antivirus. Mine is bone stock firmware, 5.0.2.