Custom plugin based on groups


I'm adding a plugin for something akin to groups - but with different layouts etc. Lets call it an 'issue'. it will have members (invited only), forum, polls etc - but needs to be laid out and administered differently from groups, and will have custom permissioning.

Looking at the dev docs, it appears that customizing based on Elgggroups is the way to go. So I've started playing with a test plugin - based on what I can see in the standard groups files.

When creating such an 'issue' record, is it right to call something like $issue = new ElggGroup(); but then set it's sub-type to something like 'issues'? The reason I'm not sure is that even with this set, would the standard groups plugin still be able to view and process these issues (which i would not want) - as it's still a group record, and the group code seems to handle all group entities with ALL sub-types.