Required fields and Sites

Yes.

As you have the editable grid that gets some data and you want to store it or process it, it should be added as a start form to that process and incorporated as an action in the site.

You have two options:

1. Add interface as a process start form and add this process in a site page as an action

2. Create an interface and start a new process when clicking a button. Here, you need to add the interface directly to the site page.

Well, technically you could configure that button to validate without submit and do all things inside an interface. But that's not the way Appian works best, so the answer is "Yes".