I cannot come up with a newnew general rule that will give you the right answer in every case. Ser for permanent sates, estar for temporary ones, or perhaps better, as André Lemos puts it in his answer, ser for essential features and estar for accidental ones, is the best I am aware of. But I can clarify most of your examples. Note that I'mI from Portugal, and while I’m not aware of differences between Portugal and Brazil is this respect I would be surprised if there weren’t any at all. Note too that in some of my examples the other verb might be acceptable in some circumstances, but if you stick to the rules below no competent native speaker will tell you off. I hope this helps.
Location. – Basics Use ser for things that are intrinsically immobile. So a cozinha é aqui (you've got that one wrong), unless you're talking of a portable kitchen. Onde é a festa? because a festa takes place in one place. The festa itself is temporary, but while it lasts it is in one place. So the same applies to a reunião or a jantar andor events in general. NowFor events ser is the only option, but for other things you can substitute ficar for ser: onde fica a cozinha? Manaus fica na Amazónia.
Location – within sight. Suppose you’re looking round a square for a small shop you’ve been told is there, and you can’t find it, and are becoming impatient. It will be natural to say onde está a [optional expletive] loja? as if you were looking for a cat hidden in your living room. And someone might reply, está mesmo atrás de ti! In general you can use estar to indicate something within sight. Ser and ficar can also be used in these situations, but estar feels almost the exceptionsmost compelling of the three.
Location – surroundings. A comment below gives the example a casa está/é no meio dum bairro problemático. In this case está ou fica sounds definitely more natural than é to me. The ex-post rationalisation I can come up with is that you are not giving the location, with is an essential feature of the house, but only the sort of surroundings the house is in, which could change in theory – the neighbourhood could become less problematic. It will be the same if you say a casa está no meio de um bosque. If there were only one bosque, then it would indicate the location, and it would be more natural to say a casa é no meio do bosque. But Fica is more versatile and fits well in both cases.
Location – here your are. Aqui está or cá está is an idiomatic expression used to show someone something. So I could drive you to the shore and say, with a sweep of my arm, aqui está o Oceano Atlântico, or, when showing you around the house, aqui está a cozinha (we use this especially for things of some significance, or when you’re eager to see the thing, so it shouldwould have to be some kitchen). We could equally say aqui tens a cozinha.
Health states/diseases. Use ser for chronical conditions, estar for diseases you expect to go away. So ele é diabético, because if you have diabetes you typically have it for life. Same with ele é asmático or ele é esquizofrénico. But ele está gripado because you expect the gripe to go away after a few days or weeks. In fact for most diseases you don't have an adjective and will say ele está com/tem febre/sarampo/pneumonia.
Young/old. You use ser as you know. I suppose that’s because that does not change overnight, and does not change at one’s will; you just age according to the laws of nature. You think of someone's age range as an essential, not accidental, feature of that person. Note that for inanimate objects we can use estar. O carro está novo if it is in top-notch condition despite its age. Same for a house or a shirt. You can also say of a person ele está muito velho to mean that he looks unexpectedly old given, say, his actual age or his appearance last time you had seen him.
