I cant see well the connectors (and i dont know them well enought), but looks like the antenna connectors used in many old "dumbphones"
Incase is that... it was an standard years ago, i thought it was not much used nowadays but it seems that router uses them
Anyway... is nice you have the antenna conectors soldered in it because it should not be much hard to find a cable for them
The point is that cable should have an RP-SMA connector at the other side (i know this connectors a bit better), they started being used in USA first and the rest of the world was using different connectors, but it seems at some point the RP-SMA won the battle
If you take a look at some shop for wifi antennas, probably most of them are going to use that RP-SMA connector
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Btw, is nice the manufacturer soldered that 3 pins for Tx, Rx, Gnd... thats what you need to connect by terminal (for things like changing the bootloader, unbricking, etc)
And the first "mod" that comes to mind while looking at the board is the other 4 "holes" inmediatly under the pins (GPIO4, GPIO5, GPIO45, GPIO46)... they can be repurposed by software (modifying a setting file) and can be used for many things... one of them is you could use them to connect a SD/microSD card
Actually, instead of soldering the card directly you could solder a microSD card slot, this allows you to replace the card at any point
The idea is to use that microSD card for the system files (not for media storage)... this allows you to install many software without need to write in the flash chip

You know... the OS (and a swap partition) in the microSD... and the games and other stuff in USB
Im learning about it, im going to do it in one (or more) of my routers because i ripped that microSD slots and some low capacity microSD cards (500mb or 1gb) from a few dumbphones i have that was waiting for some butchery