Beginner Balcony Gardener. Need to know what I’m doing wrong (pests, seeds not sprouting, etc).

Over the past to years, I've started doing some light balcony gardening, mainly just a few railing coconut coir planters and a stepladder-like planter

However, I've had mixed results each time. I've had plants either fail to sprout or grow, and those that do grow usually get overrun with pests like caterpillars that chew through every leaf, or completely overrun with aphids, stinkbugs, or similar infestations. I've been trying to grow both flowers and vegtables but I've had difficulty with both to varying degrees.

I've been using an all-purpose soil, but should I be using specific, dedicated soils for my plants? Could it be that they're not getting enough sunlight in the balcony, or maybe it's a problem of me either watering them too much or too little. Furthermore, I'd like to know if there are any steps I can take to be more proactive in preventing any infestations so that I can protect my plants.

Any and all advice and protips are appreciated!