hi sir im a senior prestashop developer , i had many professioanl modules in prestashop like megamenu , custom addon's , admin customistion and fronted modules, so your module will manage virtual prodduct in prestashop, we can create assign for each graphic a the attributes colors , categories (free,licenese,...) and manage download with prestashop core classes , the module must work with orders classes and invoice classe and product class .
so your module can take 7 days of working
best regards