Oh man to be honest even just learning to make them myself is quite the journey. There is very very very little documentation out there besides what adobe provides and maybe some stray open source plugins on github so it's quite the task to learn and get up to speed considering pretty much every plugin programmer out there keeps their trade secrets to themselves. It's a pretty weird atmosphere to be in.
You can get the SDKs here! There is a PDF there that describes the overall API and includes some samples for the many different plugin types.