Method to disable plugin when requirements aren't met

I'd suggest declaring an application service which will do such check and contain information that conditions are met - and then provide it for the other parts of your plugin.

You may also try to register ProjectManagerListener or ApplicationLoadListener to do such checks

There is a PluginManagerCore.disablePlugin(String id) method available but it may require a restart of the IDE.

Would I then need to call out to the application service in all the inspections, toolboxes etc, to see if it's disabled for that project and end the operations if it is?

If the condition check result will be performed once and cached, that'd be not a problem.

I assume that such conditions may be fulfilled in the next IDE run or when another project will be opened, right?

Yes, it's possible that across the projects opened, some will fulfil the conditions and some won't. Great, I'll implement like that then, thanks.

So if conditions are project dependent, use projectService instead of applicationService.

I currently have a project component, as per 

<project-components>
  <component>
    <implementation-class>

Should I migrate this to a project service?

Plugin components are deprecated now - check our docs about Plugin Components. The proper way of the implementation is linked in my first answer.

Cool, I'll do that, thanks.