Build a collectibles Funko website on Shopify

Hello! I am looking to build a website for my business, there is a few things I need on the website. Firstly this website will be built on Shopify so most of the work is already done, what I would like to do is to be able to purchase collectible figures by offering customers an immediate offer on the item, for example; A customer enters my website, they want to sell a collectible figure called boo berry metallic, so I want a page that lets them type the name of the pop, the asking price that they want or an instant sell no matter on the condition for 40% off of the value. I would also like to have an option to buy a lot of collections not just a single collectible figure, to do this I think we would need to be able to somehow integrate this websites statistics: [login to view URL] I need ideas and I need someones help with this. So important points to remember 1. I want to be able to integrate a system where I can buy peoples collection and a page where I can see all the offers I got and accept or decline accordingly 2. I want a possible way to integrate poppriceguides system legally 3. If 2 isn't possible, other ways to buy and sell collectibles, I want to do both but at the moment I need to build inventory, so buying is the main priority