I do really not know how to explain further to meet the "need more details".
To subscribe to a bot, is basically the same as the function to create the shortcut. Which you have already implemented in the official plugin. It is a perfect functionality to have in the construct plugin, since it is an easy call
UpdateAsync, is already implemented in official plugin, but only the leaderboard. What we need is the Custom, as well. So we can specify a message and a picture. This is very similar as ShareAsync.(Currently everyone has to use via Browser>Javascript for this)
ChooseAsync
needs a trigger to see if we acutally trigger a change or not. But this is a vital function, since IG basically are built on contexts. With leaderboards, updates and all. So then chooseAsync is used to switch. This needs a callback to see when it is resolved. Now we use browser>javascript, but is not perfect since we cannot see if we actually did a change.
You can see macubes plugins, his actions are the way to go!
switchGameAsync()
super easy without any callback
this we also have to do via browser>javascript currently
getSupportedAPIs()
this returns values from the API of supported features. maybe a bit to investigate to include.
I think you can have a look at macubes plugin, it is perfect for some of the events. and a good starting point for the others