The generated CSS covers the flex container's properties (direction, justify-content, align-items, wrap, gap); individual item styling (like flex-grow) isn't part of this tool's output.
Yes — adjust the preview count to see more or fewer sample items at once, useful for checking how your settings look across a larger or smaller set.
Yes — adjusting each property live and watching the preview update is a common way to build intuition for how Flexbox properties interact.