The banner approach wouldn't work in that case. I can't think of a way to added entitled articles to the top-level collection in a way that would be a good user experience. If you try a workaround such as creating a single-article collection set to Content View, that still wouldn't work when you add that collection to the app menu, because launching a collection from the top level always displays the browse page, even if Content View is selected. It seems like the best approach is to add articles 3-4 to an entitled/restricted collection and add that parent collection to the top-level.
Article-level entitlement isn't on the roadmap. Without knowing more about your app, it's difficult to make recommendations. When you say you want to add entitlement articles on top-level, are you referring to the "home" collection or the top-level collection? If you need to add entitlement articles to the home collection, one possibility is to add them to a restricted (or entitled) collection, and then create banners on your home collection that use navto links that jump to the restricted articles. Users would then tap the banner card and sign in to view the restricted article.