Subdomains are not a must. However, your titles will kill you. "101" - it doesn't mean anything to a search engine. "tips", "information" -> those mean something. If you have products, make sure to add "buy" or "purchase" or any such keyword which screams "transactions". You don't have it right now. tl;dr: Help the search engines to categorize your silos properly. Same goes for subcategories.

Good luck.