Fixes to existing code of the website in WordPress

I have a website in WordPress where there is a contact form with multiple questions, some of them are drop downs, one particular is auto populated with possible answers depending on user selection in a previous drop down. Some fields are mandatory, so on SUBMIT the form will return an error BUT the 2nd drop down is no longer visible nor the selection that someone made making it confusing to users. I need this fixed so that on SUBMIT the selection user made is "remembered" by the website. Alternatively, the button SUBMIT could be inactive for as long as mandatory fields haven't been filled out. I have a small budget as this is a small job but it will require someone with knowledge of php, CSS and JavaScript. I have more projects like this with small enhancements or maintenance needed so if all goes well with this project, there will be more to come therefore I'm looking for longer cooperation. BUT, I will require NDA to be signed (as I am also bound by one, so will need one, too).