Since you have different sizes and styles of containers, they are going to have different watering needs. since you are able to run different zones, you might want to pair like containers and put them on one zone and do this with the rest. Do you have one sensor or multiple sensors? is the function of the sensor to stop watering if it senses rain or to stop watering when the proper moisture level has been reached?

As far as sampling the pots, I find its more trial and error, tweaking the system till you are satisfied that all plants are receiving the proper watering. Of course this will be constantly changing due to environmental conditions and as the plants grow, so will their needs

Penscacola grower is right down the road from me and is spot on. On of the best ways I have found to water is to run different dedicated systems focusing on redundancy. Ex running a misting system with micro irrigation sprinkelers on a timer with water sensor and then running an independed drip irrigation that way you can fine tune each plant. Ex tomatoes, melon, etc run better when the foliage isn't wet so design the systems around each other and the plants. Personally with orchids micro sprinklers are great because you can hit a lot of the roots system in a pot.