You should let the defaults do their job, but they don't do very much. HTML's main semantic is to give things a hierarchical structure. Visually it's a free for all after that
https://developer.mozilla.org/en-US/docs/Glossary/Semantics#...
no no no, different elements have different behaviours. for example, a button automatically has accessibility features like being able to tab to it and select with Enter key, which is essential for a screenreader. do that with a div and you end up building the functionality from scratch.
if all you care about is the visuals, sure, there's little difference, but once you scratch the surface you will have a poor product by not using the correct elements (where there is a clear "correct" ofc, sometimes it's subjective).