A myriad of different whirlpool designs exist. I’m not sure if I am reading your post correctly, but 250 Litres is exceptionally small. Of course, I have no idea of your business plan and production projections, but as a microbrewer I would design a system 10 times that size. At 250 Litres you could probably whirlpool manually with a large paddle. However, if a system were to be designed, I would start with a kettle that at kettle full has a wort ratio of 1:1 for width and height. A system this small does not warrant the costs of a boiler so I would create a direct fired kettle. The bottom of the kettle should appear flat but have a 2% fall towards one side that will be your ultimate draw off point. As far as the whirlpool action, I would install a tangential in put (or a 90 degree input directly above the ultimate draw off) and I would position it about half way up the kettle. I don’t believe it matters which direction you whirlpool, but the southern hemisphere would dictate a clockwise rotation. You will want to throttle the flow so that you do not exceed a velocity of 5 m/s in your pipes. I would use the same pump that is to be used for the casting of your wort though the heat exchanger. As for the top, I would give it a domed top to aid the performance of a C.I.P. spray ball and I would give it a man way along with a vent stack. Finally, make it out of stainless steel, insulate the sides, and lift it at least a meter off the ground. Its amazing how many times it seems necessary to have to crawl under all of your equipment. A picture is worth a thousand words. It’s difficult to draw up a plan without a sketch.
Drink the beer, destiny of the land.