There was an unexpected problem on the custom clearance process which caused a lengthy delay.
Anyway, the parts have finally arrived. I put all of them together and managed to get the gateway up and running.
Since Indonesia is currently using 923-925MHz frequency plan then we need to find a gateway and antenna that operates in those frequency channels.
Putting all together
I managed to build a simple backplane (Eagle CAD) for the Raspberry Pi that I put in TTN Surabaya github page: github.com/ttn-surabaya/RHF0M301-Pi-Adapter
Also, You can find the wiring configuration and a simple explanation of how to build the gateway there.
Please notice that this gateway is currently under test, so you might not see the gateway on the map all the time. I am planning to put this gateway outside once I found a good and high place in Surabaya. Any suggestions are welcome and appreciated.