For question 1. I beleive that is the default for the php ini file. If you are using the mail command in php, you can set this yourself in the php script.
$header=‘From: yourname email@example.com’;
mail ($to, $subject, $message, $header);
For question 2. When you submit a form, the form passes values to the script. The script can check the values to verify they are correct or not empty. You can assign those same values to your form or you can just use echo or print the values. Your choice. I prefer to assign the values back to the form. I just think it looks better. If you have an html book you should beable to find default values for forms. Assign the values as the default.
You could just create a thank you page when someone completes the form, then they know the form was sent. If you do so also create a page that will display if they forgot to fill something out that is required. This way you will know the form is working.