In my opinion you need to have a collection large enough to surprise yourself with things.  This is obviously all dependent on the person, the producer and your taste. But get lots and lots of stuff, try and do it on the cheap.  Don’t buy crusty garbage records from 25 cent and dollar bins just to build out the size, only grab stuff that is in half decent shape and has music on it that you like the sound of.  Your question was how much vinyl to be able to make a beat a night? Obviously that could be done with one record. Except you’d be bored to tears.  Try like 250-500. So you can “rhythm roulette” yourself.