thejager if you run the installer via the web, it should use the same shell user as during regular forum browsing. We don't have any special logic for that, the shell user is configured in the webserver.
It's possible to run the Flarum installation via the command line as well, in which case you might end up using a different user, but it doesn't appear to be what you did here.
The assets are not published during installation. They are published when you open the forum for the first time if they don't exist (or every time if debug mode is on). You can force the assets to be re-created next time by clearing the cache with php flarum cache:clear and visiting the page. You can manually re-publish the static assets (fonts, images, but not the main Less/javascript) with php flarum assets:publish
If you absolutely need to generate the Less and javascript server-side (usually for performance reason or as part of continuous deployment) you can use this package https://discuss.flarum.org/d/23321-cache-assets
If no logs appear in the storage folder, try setting debug to true in config.php and try again. Errors will be shown on the page. If there's a file permission issue, Flarum might be unable to write to the log file either.
