Like you said, it seems like the functionality already exists in existing modules.

Some of the stuff, maybe not. But overall you can simply create a group and limit a page / module security setting to that group. So, for instance, you can create a group called "Tree Lovers", and then created a "Tree Lovers Page" and add an instance of the forums module and set the security to just the "Tree Lovers" group. All other forums on your page will be left alone, but the one on the "Tree Lovers Page" will only be accessable to that group.

I don't think you really want to put together a module that handles all of that, but learning how to stitch the security pieces together will provide you with a lot of functionality.

Thanks for replying. I looked at smart-thinker's UserGroups module quite a bit, but it doesn't provide any of the functionality I'm looking for beyond making groups.