Build me a referral system online

hi, I'd like your help to develop a referral system and integrate with billplz (local Malaysia Payment Gateway) for me to pay sellers online. This platform allow seller to post their documents (winword or pdf) and name of the prospect, contact details, commencement date, budget expectation, the current cost per month, any other costs, buyer (myself) will verify the document, and then I will make payment via billplz or senangpay - if the job is completed. For seller, they will need to go through the verification process, their name, age, profession, their linkedin profile, for them upload their CV (Resume) and for me to interview first before going onto the platform (website). They can sign up or register via linkedin or their personal email address. There should be a code verification via email. And notify me if there is a new seller signed up. Me, as the buyer will post a job, the name of the job, the target date to complete, the job cost I will pay once completed, and all the seller can bid online and offer their cheapest cost for me to select, and then when the job is complete, i will pay. Then I need a API created for this website to be connected to another website (many tracking systems). Instead of me posting the job, another system can push the 'job order' to this website. allow me to have a chat box for me to communicate with the seller. Thanks, Calvin.