Change and optimize website structure from scratch

I need help to program my website from SCRATCH. It is a wordpress site with WooCommerce installed. It is very bad programmed and the structure is not good. Codes are writing eachother over and it is not optimized. The functions and the style of the website is GOOD. But there are some bugs that are appearing because of the bad programming and multiple different stylesheets. There are 2 child themes etcetera. I want to keep the website EXACTLY like it is but to program it correctly in the files. I want to be able to update wordpress, woocommerce and plugins without and issues in future. I also have some things that are needed to be done after the website has been programmed correctly. I will attach these images. If PSD-files are needed to get some properties then I will give you them also. But note that I want the design exactly like it is now. The website is correct responsive now in ALL versions, mobile tablet etc. I want it to keep it that way and not lose any properties. ___________________________________________ List of work to do from scratch: 1. The first thing to do is to fix the website HTML structure. This means that we don’t need to apply css separately for all pages. At the moment we need to do that, which is not correct. So please fix the whole HTML structure. 2. Proper setup of child theme. It is not needed to setup two css or two of the same file in both themes. We need only 2 css, 1 for main css and second for responsive. Make sure that all responsive media query should manage from [login to view URL] not from main css. 3. Make the structure perfect so that that Ajax and JavaScript does not affect any other code. 4. Do not use more plugins, it conflicts with the JavaScript. See if some plugins can be removed. 5. Don’t put any commented code in files. It defects the website speed and try to make code clean. 6. Don’t use display:none css for code hiding. Remove from the files directly if it is not needed. This means we can optimize the website. 7. Make sure you coded the functions only in required files and not in too many files. Feel free to ask if you have any more questions. ___________________________________________