联系表单与文件上传器解决方案

I'm building a website (no CMS or framework) that needs a contact form with a file uploader. I've already written a PHP script for a standalone contact form, but I'm not sure how to go about connecting it with a file uploader that will store the files on the server and will also work on mobile devices.

Since I'm not very experienced in this topic, my questions are:

1. Would this be too difficult to manually write and implement?
2. Are there any existing solutions I can use?
3. Considering the website is almost done (structure/design have been built), should I switch to WordPress and use a plugin? I got 3/4 into converting the HTML into a theme, but I'd really prefer to continue this way

Any advice would be greatly appreciated. Thanks!

Uploading files without a framework is made quite easy with w3's guide:

http://www.w3schools.com/php/php_file_upload.asp