Is 1 dripper enough per plant?

Depends on the dripper.. if not distributed well enough in a larger pot, it can be an issue. On far side, after an irrigation, go investigate how deep you have to ppke down at far edge before you feel moisture. That will give a good idea of what proportion of the substrate is getting moisture. if soilless, with less consistent runoff going through entirety, may need to reduce concentration a bit -- observe and react. Just be on look out for early hints of overfeeding. i use five gallon pots tha ar about 11.5" wide at the top and 10" wide at bottom and 11" tall. I use the emitters that spray out in 8 directions. I have the pressure to give about a 4" diameter. I use 2 per pot and overlap them as evenly as i can. The 2 dryes points are at intersection of the two circles of water.. top 1/2-1" can remain dry in that small spot on each side of pot, but overall.. fairly consistent and haven't had issues in 2 years now. Not saying this is minimum, but just 1 data point to consider as you go forward. If it works, it works. That's the most important thing.