From the economic perspective its quite narrow minded to just focus on the port revenues. Vast majority of future revenues will come from supporting activities around Gwadar port and the city. Government revenue will come from: selling/leasing land, fees, JV with foreign firms, tax revenue from workers in industrial zones and supporting roles (ie. truck drivers, tradesmen), tax revenue from companies that are involved in the construction and support (food, services, finance, retail) of Gwadar city. The opportunities for revenue is endless when there is an economy.
The goal is to transform Gwadar into a regional trading hub and industrial zone much like Dubai, Shenzhen, and Shanghai.
"For instance, in addition to the preferential policies of reducing or eliminating Customs duties and income tax common to the economic and technological development zones, the state also permits the zone to allow foreign business people to open financial institutions and run tertiary industries." - Shanghai Pudong New Zone
Gwadar port is important not for its port revenues but for the opportunities it opens up for Pakistan. Be mindful of the bigger picture. The port will attract investment enabling an export driven economy for value added activities and eventually helping Pakistan to be industrially competitive and vertically integrate its supply chain. Workers will get paid and their salaries taxed, workers will buy homes, consume goods and services, new business will start to support the city and access international markets. The port will have a great multiplier effect on the economy.
In the future the easiest way to make money in Gwadar will be in real estate/construction not the port.
Although the port is strategically important, it will play a small role in revenues compared to the Gwadar city project. Despite being the largest port in the world Port of Ningbo-Zhoushan only makes $420 million USD (profit) a year while moving 889 million tonnes of cargo, which is $0.5 USD per ton. At $1.6 billion USD Gwadar will need to ship more than 3.2 billion tons of cargo to break even. Over 40 years Gwadar port will need to ship more than an average of 80 million tonnes a year.
The profit/ton probably already contains the financing costs of the port. If we assume its included then if Gwadar matches Karachi's yearly tonnage of 65 million tons then the profit would be $32.5 million a year. As port technology gets more advanced with greater automation, the cost per ton will decrease further. There are a few berths in Port of Qingdao that's automated (a few people in the control room), currently capable of 1.5 million TEU and 5.2 million TEU in a few years, currently Port of Karachi handles 1.5 million TEU. The more efficient the port the more goods and industry it will attract, seeking high prices from ports will destroy industry.
https://www.porttechnology.org/news/asia_enters_fully_automated_terminal_era
https://en.wikipedia.org/wiki/Port_of_Karachi
Ports don't make as much money as people think.
https://finance.google.ca/finance?q=SHA:601018
https://en.wikipedia.org/wiki/List_of_busiest_ports_by_cargo_tonnage
In an efficient industrial system ports are more of a support utility for exports. An efficient port will make Pakistan's exports and Gwadar as a hub a lot more competitive in the global marketplace.