they were 21 weeks yesterday.
Are they laying yet?
Point-Of-Lay pullets tend to spend time exploring possible nesting sites so if they are about to start laying they may be checking out the boxes and getting comfortable with them.
Do they need feed in their coop? If I put the food in, do I need to put water in too?
This is a matter of personal preference. I don't like food in the coop because I want them to be outside as much as possible and because my current coop is relatively small. I built a shelter for the feeder and waterer so I can keep them in the run: https://www.backyardchickens.com/articles/an-outdoor-shelter-for-the-feeder-and-waterer.76487/