@LucianoR 

what tplink sells in china does not work with anything sold in the rest of the world. don't try it. 

if you say you want a dummy switch, you can consider it but the warranty is different.

what you asked, from my experience in tech stuff I can answer some.

1. impossible. you posted other details. ports are different. then you won't be able to use it with the omada controller

2. firmware is made based on the chipset. you certain the chipset between these two are the same?

if they are using the same chipset, ram is similar, you probably can use the firmware and flash it. i played with asus and some other brands using the same chip. it may work if the chipset is the same.but that'll void the warranty certainly.

3. no

4. probably you can give it away to someone who does not need a controller. just use it as an ap.

go with the same product line. it's common for many manufacturers to make different software or localized software when they go for a different market. things would be entirely different. 

  @LucianoR 

it's just another set of commands/kernel. if the kernel is different, it will not work that way. no way to fix this or mirror it. 

  @LucianoR 

if they share the same CPU, you have a chance to flash the firmware to it. but not sure if you have/can access the root to do that.