Pins 10, 11, 12, and 13 on the Stalker are used by the SPIbus, so if you’re want to use the microSD card socket, you can’t use those digital pins for anything else. It’s been awhile since I looked at the specs of the Stalker, but I think there are very few free pins. That’s one of the reasons we stopped using it and created the Mayfly. And the Mayfly’s secondary hardware serial port makes it easier since you can sometime avoid using the SoftwareSerial functions if you just have one serial device to interface with.
The Mayfly boards should be available again on Amazon by this weekend.