You can have as many keggles as you want
Spend some time researching old school pro brewing systems. You can have one keggle just for heating and containing hot water (Hot Liquor Tank). You can have one just to mash in (Mash Tun). You can have one just to lauter in (Lauter Tun). Most smaller systems combine the mash and lauter in one so you have the Mash/Lauter Tun (MLT).
Then there is the brew kettle (BK). You can have a separate whirlpool tank but again, most combine the whirlpool in the kettle. For cooling, breweries used to use cool ships to allow the cold break to settle before being forced cooled with plate heat exchangers.
Now, most whirlpool in the kettle, allow to wort to rest from between 10- 45 mins and then force cool and send it to the fermenter with in-line oxygenation.
If you are using an immersion chiller, it might be a good idea to have the whirlpool outlet on a different vertical plane than the inlet. This way you can reduce the amount of temperature stratification. Or you can avoid it altogether and use a Counter Flow Chiller on the fly into your fermenter.