Design team makes a mock that is styled and placed correctly, including moving around exiting elements in the page.

> a datastore to store the uploaded values

Just 1 datastore? More like:

+ a frontend service to get/put and validate the data is in the right format with sizing

+ a backend storage service (hardened because we don't know what's in the document) for get/put with sizing and validation

optionally - an integration into a legacy feeds system to get the spreadsheet's data to all of the places it needs to go

Ensure Legal, ADA, FDA, whatever compliant.

Document EVERY decision along the way and coordinate.

3 weeks looks a little hight to me, but things tend to go awry with so many moving parts.