Help finishing e-commerce site in Squarespace

Retail Natural Stone Project is 80-90% built by myself in Squarespace however to complete I need someone who is confident and experienced in code injection or creation to fulfil the following objectives: - bespoke quantity calculation at checkout to allow for part quantities ie we sell in psqm but each pc may be 0.54 sqm so code needs to allow for calculation - Coverage calculator function for customer to be able to calculate quantity required by putting in dimensions and allowing for 10% wasteage - Add 'Request a sample' button and ordering - Custom Invoice creation - SEO (possibly as add on when above complete) - Test and pre launch I have sample competitor websites to exemplify the above. Message if any queries, immediate start required. Fixed Price based on estimated hours preferred.