Hotel/Hostel Booking site with a forum - App project

Mobile app project description

I am trying to build a website that is similar to Airbnb/Hostelworld where the guest can book in Homes that offer both private rooms and common rooms where there can be anywhere from two to several beds (I would like it to be booked per room for private rooms and per bed for shared/common rooms). I would like the home owners to be able to set their own security deposit amount and when the guests need to pay the remainder. Either before arrival or once they arrive.
I would like the guests to be able to write reviews only if they have stayed there.
Also, I would like to have a forum where guests can talk, build there own chat topics and chat between each other privately in a messenger.
I am also looking into booking tours that would be appointment based.

I have found many Airbnb clones and Wordpress themes that have what I want but just needs to be modified. Looking to see how much it will cost to do this to see if it is even worth persuing as a start up company.