Start with the task
A marketing website helps a visitor understand an offer and take the next step. A business application lets a user perform operational tasks under rules, roles and permissions. A project can require both.
Clarify the boundaries
Before estimating, name the users, the actions they need to complete, the information they can access and the systems involved. Then distinguish public content from authenticated workflows.
Connect without duplicating
A website, web application and mobile app may share APIs and brand assets. The delivery plan should identify that shared work once, while giving each experience appropriate design and testing.
A useful first brief
Describe the audience, the five most important tasks, current constraints, existing tools and desired launch window. That creates a better starting point than a long list of frameworks.