Read This Post: Why you should create a webpage for your WordPress plugin
A dedicated webpage for your WordPress plugin gives you more credibility in the flooded plugin market and give your users a place to get help. So why haven’t you created a page for your plugin?
Read This Post: What a custom functionality plugin is and why you should use one
A lot of tutorials have you put custom code in the functions.php file. But if it affects WordPress itself in anyway, that code should really go in a functionality plugin.