A daily range from your weight and goal
Requirements shift with body composition, training volume, age and total calories. Research almost always reports a band rather than a single figure. Starting at the lower end and adjusting to how you respond is the practical approach.
Splitting intake across several meals is generally considered more efficient than one very large serving. That said, the daily total matters more, so hit the total first and refine the distribution after.
Not if food already covers it. Powder is a convenient way to close a gap, not something with a special effect of its own. Counting what your normal meals already provide is the useful first step.