I want to build a membership website that offers project & thesis writing services with the following features/functionality:
• clients will be able to register/login into their dashboard
• A financial system where clients will be charged based on the volume of their work i.e. t e no of page and number of days for their job to be delivered.
• A market place where members can upload the works for sale (after the sales, they can view the numbers of sales in their dashboard and their amount earned and also a system where our commission will be deducted and the balance will be shown on the clients area for withdrawal. There will be a payout request functionality)
• Online payment API I have a fair knowledge about PHP and beginner in python.
Which language should i use fr this project?
and which area should i focus for the course of this work?

Html, css, javascript, Php/mysql

Ensure you structure your database and u put on paper, the layout of the website and clear algorithm on how each section will work very well before you start the real work coz it will save u a lot of time and stress during the process of coding.