PHP - Is This Bad Practice?

Hey everyone,

I am working on a project for fun. This is a LAMP application that is going to run on my intranet server, and hold NO VALUABLE data. I am doing it just to get better at programming, and learn some best practices and techniques.

at this point, I am working on some things, and I don't know what the best practices are. Can someone help me go down the pest route? 

1. A log-in system and I want to include a "remember me" button. What is the best practice for this? Obviously leaving user data in a cookie is asking for trouble, so I was thinking of leaving a unique id of some sort?

2. Information in a login SESSION. What information do you put in a log in session? I have seen lots of different techniques on this. I don't really know which is the best. For the moment, I keep an array like this: array('Status'=>True, 'Username'=>'Users name"  ,'email'=>'users Email'). If a hacker can inject session information, this seems like it would be really easy to break, because they only need a user's name and email to gain access. Is there something more I should do?

3. Config file that holds Mysql Information. I made a file that contains all the values that might change over time. That way I only need to change it in one spot. In this file I have things like the Mysql Database information. Should these files be encrypted? Or can I use a .htaccess file to make sure it isn't accessible to a hacker (as I mentioned before, this isn't a project that's going live, its more of an exercise to help me learn)

Thanks everyone

2 PART QUESTION (so I don't have to ask two questions 😀  )

1.)
My script has tons of PHP variables. Is it better to declare them all at the top of my page like this:
$cat = $words = $day = $lunch = $user = $address = $potato = $_SESSION["goodpeople"] = $dumbquestionList = $b = $hundredMoreVariables = "";
-or-
as needed, like this:
$cat = "";  if($day == 'Thursday') { $cat = 'time_to_feed'; }
$words = "";  $school = array('teachers'=>'boring','lunch'=>'free'); $words = $school['teachers'];
$_SESSION["goodpeople"] = ""; if($_SESSION["goodpeople"] == "" { $_SESSION["goodpeople"] = 'Gandhi'; }

2.)
What are the pros and cons of declaring variables as NULL and using " isset " versus declaring variables as "" and using ==
Example:
$cat = $words = $day = $lunch = $user = $address = NULL;
if( !isset($cat)) { $cat = 'black'; }.........................if(isset($day)) { $sleep = 'none'; }..............etc., etc.
-or-
$cat = $words = $day = $lunch = $user = $address = "";
if($cat == "") { $cat = 'black'; }............................ if($day != "") { $sleep = 'none'; }................etc., etc.

On my particular coding, I can use either the NULL/isset style, or, the ""/== style, with no errors or ill effects.... but something tells me the expert PHP coders prefer one over the other...

Thank you!!

<?php
// --------------------------------------------------------------------------
// ADMIN BAR HANDLER
// --------------------------------------------------------------------------

/**
 * First we need to determine if the user
 * is logged in or not. After determining
 * the user's logged in status, we will then
 * choose to display the admin bar or
 * redirect the user to the login page.
 */
function admin_bar()
{
	if ( defined( USER_IS_LOGGED_IN ) )
	{
		echo "<div class='admin_bar'>
					Admin Bar Here
				</div>";
	}
	
	else if ( defined( USER_IS_NOT_LOGGED_IN ) )
	{
		header( "Location: " . LOGIN_PAGE ) ;
	}
}

?>

public function DisplayHeader()
{
    ?>
    <table width="100%" cellpadding="12"
    cellspacing="0" border="0">
    <tr bgcolor ="black">
    <td align ="left"><img src = "logo.gif" /></td>
    <td>
    <h1>TLA Consulting Pty Ltd</h1>
    </td>
    <td align ="right"><img src = "logo.gif" /></td>
    </tr>
    </table>
    <?php
}