anhnd0410 welcome to Flarum !
Flarum is highly extensible, so changing the layout can be done by anyone familiar with Flarum extensions, though it could be a lot of work depending on the target. I don't think there is any existing extension to display whole discussions or posts on the homepage. The closest we have are the discussion summaries extension that enables summaries for all discussions, instead of just the pinned ones.
Some simple customization can be done via CSS, but this won't allow adding things that aren't already on the homepage.
You can have a look at the Flagrow Upload extension to add file upload to Flarum.
We've seen forums perform well with many discussions, but you will probably want to do your own tests. A bare Flarum is usually pretty fast, but the more extension you use, the more performance issues could arise. If you notice parts of Flarum or extensions whose performance could be improved, please let us know, we're always on the lookout for possible improvements!
You can see some large forums already use Flarum https://builtwithflarum.com/
If you plan to use Flarum in production, keep in mind our beta warning at the top of https://flarum.org/docs/install.html . While Flarum is often stable enough for production, you or your developers might need to get their hands dirty when updating, in particular if you use many third-party extensions.
