If anyone is looking for a really good place to get started with SDR, I'd highly recommend the RTL-SDR Blog V3:
Dumb question (and maybe this isn't legal?) but are there SDR transceivers/libraries?
It'd be neat to have a zigbee/zwave hub with my SDR so I could mix and match some stuff.
HackRF One is an option. There are a number of others. Legality varies by country/frequency/power level.
Can also make a Raspberry Pi act as a transmitter (https://github.com/F5OEO/rpitx), which could hit the zwave frequency but not the zigbee one. (Also, make sure to put a low pass filter on it.)