The brain is not a "lump of fat". If you desiccate the brain, most of what's left are lipids, yes, but at that point you are not conscious anymore. The brain is a mix of proteins, carbohydrates, water and fat.
Also fairly sure that electrical impulses alone cannot account for consciousness. If that were "all" there was to it we'd have simulated a human brain by now. There's a few theories about quantum processes being involved but this isn't exactly easily proven.
Depends on when you start the timer. The fruit fly brain was only completely mapped recently. There's a simulation of it that runs on a laptop. If that simulation can run on a modern laptop and the map was otherwise available, then it likely could have been done on supercomputers in the decades prior.
To simulate a human brain, we would need a complete map of it. We don't have that yet. If the quantum theories around neurons are correct, then the map would be incomplete without it.
I doubt we could simulate it directly without a very specialized ASIC.