As far as cleaning goes the main thing your want to do is make sure you empty out the ash after a cook so it doesn't draw moisture and turn into an ash cement clogging up your sweeps.
That greasy residue on the lid and bowl is a good thing. Think if it as your natural lid gasket.
Using foil pans, foil, things like the SnS griddle under your food does keep the mess down quite a bit. The one touch system keeps it easy, but in vintage kettles or the Ranch it can save you a lot of headache. If you want to keep your ash pan clean you can wrap the top with tin foil.
As far as deep cleaning goes most people here just do a deep cleaning when they first buy the kettle because people tend to abuse their kettles and do weird stuff like burn trash in them.
Use SS hardware, keep your kettles covered (careful how you do it in high humid areas), and just be careful when moving the kettle or removing the lid.
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