The fluffier your soil is and more sand, the fewer the holes you need. Tiny holes seem to clog up too easily so I make them about 1/2" dia. and 6 of them... just grabbing a drill bit close to that without reading what size is stamped on it. Split point bits make a cleaner hole in plastic.
Â
Dripping sprinkler will work if on a timer but you don't want a continuous drip as the soil surface should be allowed to dry out so it doesn't promote fungus or insect infestation. For potted plants I just use a plastic coffee can dipped into a rain barrel or bucket full of water, or a hose if I have one out which I usually do once the warmer months of summer arrive.