Hello i am a prestashop expert, i already created lots of Prestashop modules. you can check my reputation and previous work in my profile.
i understand prestashop's system very well.
To make your infinite scroll it only needs to create a module that will create a new page with javascript to load the remaining products on the catalog. For sharing the message, i think it is better to use cookie, because i think it is not convenience for the user if they have to share the message each time they come to your website.
please let me know what you think.
regards
kurnianggoro