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8-10w for map lights is good. Anything less and you will be disappointed.
That is around 8 SMD LEDs (and more) on the light assembly, depending on the circuitry and LED size, if you are talking about the festoon style overhead LEDs.
I look at these LED approach differently. When you put in those bright LED for parking light, it will light up the whole light casing along with the lowbeam. It seems too much for me and you don't get the distinct look of having a lowbeam and the parking light. I much prefer to see different "layer" in my light assembly.
As for interior, I thought about swapping to LED and then realized that the warm "yellow" OEM light is actually perfect. They slowly turn on/off and are much easier on the eyes. If I need to look at something, then there are those 4 bright LED reading light for each side.
Puddle light is probably the only thing I would change to LED for better visibility.
As far as making the car explode - no, those LED should be fine in the car as long as you don't mind really bright parking lights.