Hi Willy,
"Yes" to all your questions!
In the lefthand window of the easy-OPC-Configurator program you're able to add an arbitrary number of new devices. Mark the desired device and in the righthand window choose "Ethernet" as communication type and "Lantronix" as Connector. Addressing is done by different IP-Addresses of course. At the moment the only possible speed is 9600 baud.
Configure your Etherent to Seriell Adapters accordingly and you're done!
If not, feel free to ask again
Best regards
Bernhard