Sensor Network

You might just need to try it and see! (and report feedback to help others). There's zero information there to know if they can be built into a viable solution.

If you've not found any info on these items so far, I think it's unlikely anyone else has tried them, let alone know the long-term reliability of them. They are cheap enough, so it's not a lot of money to try it out. They are not going to be industrial grade products at that price.

The IOT 4g gateway already has an RS485 interface, Why do you want to use another RS485 hub? I think all what you want can be done using  https://www.cdebyte.com/products/E840-DTU(EC05-485)E

You may have to spend some time on understanding how to configure the gateway for your needs.

You will need to determine if your gateway can handle multiple addresses on the RS485 bus.  My guess would be that it supports a single node.

I agree that the need for a HUB is possibly over kill, The RS-485 standard allows for long cabling distances in electrically noisy environments and can support multiple devices on the same bus. meaning you just daisy chain your devices if they support that, the specification certainly does.

Robert Peter Oakes The ($5 US) hub looks to be a connection point that allows more of a star topography connection than the typical RS485 daisy chain.  I would describe it as an isolation/repeater.  The website shows Master to multiple Slaves so nothing fancy.

I was thinking if I had multiple sensor nodes, I could connect them to through the hub. But the problem would be if the gateway can handle multiple addresses.
I really appreciate your response!

Thank you! I was also worried if the gateway can do that. If I go for a better  gateway as in here https://www.alibaba.com/product-detail/Industrial-Gateways-Modbus-RTU-TCP-Master_1601044443084.html?spm=a2756.order-detail-ta-ta-b.0.0.54f82fc2Uya6yU,

With the hub, will I be able to connect multiple sensors?

Thank you for the feedback. I will try them out and give feedback. The aim of having these cheap module is for testing and non-heavy industrial usage. 
I will likely go for industrial versions after testing.
I appreciate your feedback.

Thank you, I needed the hub in case I have multiple sensors ... 
It is not an essential component of the architecture I agree.

corel_draw Please forgive me if I start out too basic.

I started learning this stuff by researching MODBUS RTU.  MODBUS and RS485 are not the same.  My simple approach may offend some, but... crawl, walk, run.  MODBUS is the language.  It's not that important right now.  RS485 is the hardware - an old school telephone party line your information will travel on.  You can wire one sensor to the next to the next in most cases.  Each node on the line gets a different node address (1, 2, 3...).  Your RS485 "network" will probably be Master/Slave.  The Master asks the questions.  The Slaves answer.  The Master calls the Slave by the Node Address.  "Node 3:  What data is at data point 0x0010?"  Only Node 3 answers.
When you wire it, A is always A.  B is always B.  For everyone.
Put a 120 ohm resistor (only 1) at the very end of the line to dampen any "bounce-back" of the transmission.  I liken this to a LONG hallway and all the nodes are rooms along the hallway.  If there's a lot of echo in the hallway, you'll have a hard time hearing when your node number is called.  Hang a blanket on the wall at the end to dampen the echo.

Where Gateways come in is if you need two or more Masters asking questions.  Now we need a traffic cop.  Your turn.  My turn.  His turn.  Her turn.  Repeat.
OR if we need to change transport media - say going from our little simple wire party line to Ethernet.  This is your application.
You should be fine starting out with Gateway -> Device -> Device.

You will also run into MODBUS TCP/IP.  This is a bit of what your Gateway will be doing - sort of.  MODBUS TCP/IP simply takes the MODBUS RTU data packet, wraps it neatly in an ethernet TCP/IP "box" and puts it on the ethernet network.  That network does it's thing and delivers the box where its supposed to go.  One the other end, MODBUS TCP/IP pulls the MODBUS RTU stuff out of the box and either processes it or plops it onto a different simple party line RS485 network.

I hope this helps.