The ratio is right as you have it, meaning for every 1000lt of water you need 2000lt of grow beds but 60 kg of fish is extreme number, its the maximum amount and risky! if something goes wrong u will end up with many kilos dead fish. Try less amount of fish to be more sure and calm lets say make the max 40.
I never separated my tank but I don’t think is something difficult to happen. Can tell u though from my experience that even after harvesting all fish the plants survive ok for some time, maybe with less growth ratio but no problem for 3 months I left them growing with no fish:), the water cycling through the system can use some nutrients that exist in well established systems after time.
Recently i added 35 fish and planted new grow beds at the same time, to say the truth was little bit stressed that the bacteria was not going to support the plants, but 3 weeks later everything was working perfect!! fishes and plants ok!

Thanks so much for your info! I understand now that I will need to change the pens according to the growth of the fish, and want to find solve so I can make high profits out of the story, u see I’m planning to sell the project to someone who wants to make business out of it.