question to experienced developers about functionality

I’m willing to create a website, Wordpress based with some expensive theme, however, my desired functionality is this:

I have main Facebook group, with over 500k users, and this Facebook group have a lot of sub groups.
on these sub groups we sale many different products sub_group_car sub_group_computers sub_groups_furniture etc.

right now, the people on Facebook, posting on the relevant group and people can comment on the sell product (it’s a second hand selling community). however, it’s based on Facebook and due to many of users selling it’s really hard to keep on everything since i need to scroll up lots of time and it takes me hours on hours to get for an old post.

My desired functionality is, to create this Wordpress website, with one button “sale item”, the customers will have to login to the site with their Facebook account (Facebook api), and they’ll will post through the website to the relevant category and it’ll automatically post to the relevant group using the customer Facebook account.

more over, if people comment on the Facebook, it’ll update on the website and reversed. if its possible, can you refer me to the right freelancer? i’m willing to pay ofcurse, thank you guys.