Hi there,
You can use "Software Serial Port " Lib. Selecting two pins as TX & RX
But you also can Use the Serial (usb) port and Serial1 (TX,RX) Pins 6 & 7 .
Look at your PINout Here
In this manner 3 serial ports can be realized , However memory becomes an issue with only 256k Ram
Flow control for the GPS data or good configuration and setup to filter unwanted data and avoiding buffer overruns. Check out the GPS setup I demo’d on here.
HTH
GL 
PJ