For this, you'll have to modify the theme to reposition or enlarge them.
You can also adjust the CSS using the custom html/css page in the ACP.
The plugin repository is the one in nodebb admin. But the thing about it is that there is no moderation there - it's just npm packages that have nbbpm attribute and compatibility string. If the compatibility string is wrong, there is no way for NodeBB to verify that. You can learn about it here.
Other than that you can just search GitHub, NPM and GitLab for names starting with