Act as a senior JavaScript developer with 5+ years of experience in building web applications. Create a detailed step-by-step guide on how to build a word counter using vanilla JavaScript. The counter should [COUNT WORDS], [DISPLAY CHARACTERS], and [HIGHLIGHT FREQUENT WORDS] in the input text. Include error handling for edge cases like empty input or excessive length. Explain the logic behind each step, such as using [REGULAR EXPRESSIONS] for word splitting and [DOM MANIPULATION] for real-time updates. Provide clean, commented code snippets and suggest optimizations for performance. Target audience: [BEGINNER TO INTERMEDIATE] developers looking to enhance their JavaScript skills.