By no means mining can be considered as a passive income, especially when you have more than just one or two rigs. Monitoring, maintenance, security, power issues... It all takes time and effort. And to answer your other question - no, it's not a good time buying cards now, prices are insane and profits are in decline. Rewards vary all the time due to few factors - block reward, network hashrate, exchange rate etc.
How is mining not a passive income? Is passive income not a gradual income that comes in no matter what? With mining your reward will not stays as fixed price, might be more or even lower that's the difference but you get paid always, to me mining is a good example of passive income