For the airplane data, I always liked browsing sites like flightradar24, planefinder etc, and wondered how they aggregated the data, and it sort of just went from there. I also now send the ADS-B data to open projects rather than commercial only entities.
In terms of the random radio transmissions, it was simply because I was already installing the two ADS-B antennas in my attic, and thought I might as well just put up the standard telescopic antenna that came with the USB receivers as well. I'm a newbie in terms of radio, so it's just been interesting scanning the bands to see what you can find and listen to.
A future project I have is to try and pick up the 443Mhz transmission from a really simple weather/temperature sensor I got from Walmart a while ago, since apparently that's what it uses to talk to the little base station it came with.
