Well, the galleries themselves are seen if you click on the Media tab and choose a gallery to view.
As far as having an image both in your gallery AND in a forum thread, your best bet would be to upload it to your gallery, and then link to the gallery in the thread. That way the same image is being used twice, instead of having to upload it to two different locations.
As far as threads with HiveWire products, such as Harry, you'll find all the appropriate threads for each of the products in the "It's About the Art" forum.
As far as your render only having HiveWire products, no I don't think it's necessary, I just think the main focus be the HiveWire product you used to create the render, such as Dawn, Dusk, Luna or Harry. If you scroll down the It's About the Art forum, there's a thread called "I Just Wanted to Post an Image Thread", where you can post renders of any 3D character you purchased anywhere elsewhere, such as V4, M4, Genesis 1, 2 or 3, etc.