I've been tasked with my first enterprise application. The application is fairly simple in design from a customer viewpoint. It is an online administrative portal to allow our customers to customize/change their website content. (Right now customers have to call us for changes.) All of their web page content is stored in a database and is retrieved based on the customer id. So here is where I stand.

To paint a picture of my skill set I am a Networking/Communications major with a self-taught programming background from examples, books, tutorials, and etc. I have never taken any actual classes for programming in PHP (few java classes in high-school years ago). The last time I wrote an application from scratch was with PHP4 and I was able to get through it pretty good. Since the addition of PHP5 giving OOP more depth per say I am trying to learn that right now since I've never used it in PHP. All of my past applications have been for personal use and never for a business. So you can see why I'm a bit up in the air right now (I'm a Network Administrator for a small business so I'm having to wear multiple hats now). So since I have never designed an application for enterprise/corporate level before I have some questions.

1) What is the best way to start designing this style of application? (Right now I have some chicken scratchs on paper of the initial visual design but nothing for the server side code layout.)

2) Should I go with procedural code or object oriented? (I was thinking object oriented since it would allow for easy expansion should new features need to be added later on. I'm reading "PHP In Action" right now to help learn OOP.)

Now these are just starter questions. Once I can get these answered I'm sure I will have more.

Thanks in advance for any insight and help.