It’s best to get a kit that includes 7 mics but the answer to the question also depends on the size of the room since in smaller rooms you can get more stage volume out of your drums without microphones. When recording for studio work a good setup depends a lot on what you are trying to achieve.
If you have the time and the ears to experiment with mic placement you can get very good drum records with as little as two or three well-placed mics. This method is also good if you are on a tight budget and you don’t want to go overboard with the money.
With that said, if you have a set with 7-8 microphones, not only will you get a better recording but you’ll get to learn a lot more about the art of recording which in turn will help you achieve even better results. Thus, to summarize, the number of mics needed to record drums depends on your budget and the quality of the sound that you are looking to get.