1) No, you don’t have to use BP_Component, but if you can, you probably should. It’s so much easier than trying to figure out which hooks to use. If you don’t need a particular method for your plugin (because it doesn’t have any navigation elements, for instance), just don’t include that method.
2) There seems to be a bug in the way the includes() method works for plugins. For the moment, I recommend that you include your files manually.
3) You need to call the $bp global before instantiating your class.
`global $bp;
$bp->query_subscribe = new BP_Query_Subscribe();`
