There should be a maximum of 4-6 candlesticks at the base. The less number of candlesticks at the the base the more the strength of the zone and vice versa .
other features of a good zone include :
-tight candle bases with bodies less than 50%
-strong departure , 2nd leg (IMPULSE) with at least 2 ERC candles closing at its high (about 80% of the whole candle range)
DO NOT CONSIDER A BASE WITH :
-has only doji candles but doji + gape is valid
-has long wicks , they are normally reaction to previous levels