Hello, by reading your project description I assume that you already have a Google Sheet created in which you've defined formulas to do complex calculations. You want to use that Google Sheet as a template which gets filled with data which your users will input through a webpage form on your website. Is that right?
If so, then I can utilize the Google Sheets API to insert and retrieve data from that Google Sheet. There are two ways which I know of that can be used to communicate with Google Sheets API which I've listed below and I have experience with both of them.
Let me explain: the first method relies on Google's JavaScript Client library which we can utilize to communicate with Google's servers. Google's server requires authentication via OAuth2 protocol and to make this process easier they provided their own JS Client library. It makes the process of authenticating via OAuth2 much simpler otherwise that task should be performed manually and believe me doing manual implementation is complicated and error prone. Using the same JS Client library we can communicate with any Google Apps API.
The second method relies on pure JavaScript implementation of OAuth2 without relying on the Google's JS Client library and just as I mentioned in the paragraph above its lot more complicated when done manually. Communicating with the Google Sheets API then gets accomplished using XMLHttpRequest or Fetch API whichever you prefer.
If you have any questions then send me a message.