I would like to know your opinion and experience. For me, it's ~10 stocks wich I am following closely and trade around 5 - 7 stocks.
If your strategy is a generic one and works on most markets, and if you are a long-term trader, you could trade 10s or even a hundred at a time. If your strategy works on most markets and you trade intraday, monitoring one or 2 should be good. If your strategy is market specific, then obviously trading on that particular market(s) only (ie. CL).