I can give you details of setting up the Airport but you will need to check the details for the Thecus via their website.
I need to configure the Mac Pro, AirPort and Thecus to access the Thecus locally (wirelessly)
You already have access or should do so.
The Thecus has IP on the main LAN port of 10.0.1.10
Can you please check that has not changed.
That address should be fixed as you don't want it change.. fix via the dhcp reservations in the AE or fix in the Thecus itself.
Then in the Mac simply go to finder.. is the thecus not showing in the shared area of Finder??
If not then please manually setup the network via Go, in the finder top menu, connect to server.
Type in SMB://10.0.1.10
When asked for the password please supply the password you set or default. And save it in your keychain.
If you have not setup the thecus go to browser and type the address straight in there. HTTP://10.0.1.10
The details of setting up the Thecus will all be in its manual and is outside the scope of what apple forums does.
The WAN ethernet port of the Thecus cannot use a 192.168 address.. please fix that up now and set manually to 10.0.1.254
Gateway is 10.0.1.1 and DNS can be 10.0.1.1
Then you need to open ports to it. But I do not know what ports to open.. you need to decide that..
Again the Thecus manual will tell you ports for the different protocols.
Port forwarding in the Airport routers is setup in Networking.
Here is a document for how to do it.
AirPort - Port Mapping Basics using AirPort Utility v6.x