Elxis 4.x accepts a single template for the site but this does not limits you on changing the style and layout depending on the page. We have discussed how this can be done in this forum. Here is a related post.As for the forum, the proper extension type is component. You can try make component eForum Elxis 4.x compatible although I think it is a hard task as eForum is huge... I will help you if you need assistance in something like that.
You can try make component eForum Elxis 4.x compatible...