Should I double data or power lines for UART device
Since there are no more comments here, to sum it up:
With this setup there should be one pair for each TX and RX, where in one pair there are TX and GND wires and in second pair there are RX and GND wires, but this set up will not work reliably over such a long distance.
To make this connection work properly RS-485 or RS-422 should be used,  which use differential signals.