Tried testing again today running one Pro Mini as a Gateway via FTDI/USB and the other as a node powered by the 3.3V regulated output of an Uno I had lying around. The node blinked and seemed to transmit just fine, but the gateway which was listening didn't pick up any transmissions. I played with them for a while and tried adjusting the antennas (22 AWG wire of 7.8cm (915MHZ RFM69s)) and for about half a second the gateway picked up the nodes transmissions (3 transmissions received for each payload, which means ACKs werent getting back to the node) but I wasn't able to replicate it. I'm guessing I must have soldered something wrong somehow.
Sometimes when programming a node it will send only packet every 3-4 seconds, regardless of what delay i specify, which I found strange and am guessing is something soldered incorrectly with regards to the SPI lines.
Either way, I think I'm going to go ahead and order some Moteinos tonight so that I can get started ASAP on getting the structure of my payload and basic networking framework into place.
EDIT: Reading about antenna theory leads me to believe I might have messed something up there too. As I had them when testing, the antenna was just a piece of specific length wire soldered to the ANT pin, which I figured was all that mattered. The way I am testing the transceiver is they are standalone with a bunch of long wires soldered to each pin I am using, and these wires go into a breadboard where the Pro Mini is mounted. So in this setup, the antenna of the RFM wouldn't even have a ground plane except I guess the PCB of the transceiver itself, which doesn't seem like a setup that would work. wireless is hard