I have a couple of requests to ask of you, if I may.
(1) If you can, please put the revised/new pages on the server so I can access them and see how they look and how they are coded. I have been setting them up as demo pages to see if they appeal to you and some of the HTML needs to be changed so the HTML is more consistent across the pages and the CSS needs to be consolidated into a CSS file that will be common to all of the pages.
(2) The “contact” page does not have any code on it that I recognize as a form. You will need to explain in detail exactly how a form would be used on that page and show your attempt to make one work. I can help with a form layout, but not the PHP (I am not a programmer), We have people in the php category who are excellent and would be happy to assist but they need a basis from which to work, too. A drawing (GIMP or Photoshop) might help. You might describe the form that you downloaded and why it doesn’t work.
(3) How proficiently can you read and write HTML and CSS “by hand” without using a framework? I ask because my initial impression was that you could if you had to but w3.css was easier for you. All of the work that I have been doing is outside of that framework; as such, I may be doing you a disservice if you are not able to understand and maintain the code that I am writing. How do you feel about your ability to maintain my HTML and CSS? It may be worth considering that the version of w3.css that you are using is an older version, not the current version and they are not faultlessly interchangable.
(4) Do you know how to use PHP calls to import files, such as the menu and footer? If not, try reading this step-by-step and see if it might be something you would consider.
How To Call a menu file with PHP