Thanks for trying the plugin and willing to beta test it. Here are some responses to your points

How did you install it in developer mode? I can only do it from my local development folder, which is not public.

The long time it takes to popup should be fixed in version 0.0.5. For long notes, the underline is expected to take long to appear.

You can change the language and region in the settings, for example set it to en-us for American spelling. By default, it autodetects the language. In my experience, it defaults to the US, so I don't know how you set it up.

Personalized dictionaries and pro access require more complex API queries, but is doable.

Ignoring suggestions is something I had not thought of. I tend to just ignore the red markings. I think there should be a way to do it.

Thanks