Well for one, the 24mp is overkill, I have a 60D which is 18mp and I only use it for sports because it has alot of cropping power. Other than that I use the 12mp 5d, which is more than enough. So 16mp would be plenty good for you.(I started on a 300D which had 6.3mp, it did me well.)
the 5100 has better noise performance, due to the lesser mp count, each pixel site will soak in more light, resulting in less noise.(to be fair, its only slight but noticeable)
On the weight, you are going to want a heavier camera, because once you get some good quality glass on the front-end, its going to be HEAVY. You want to have as even of a balanced camera as you can.
The new processor, eh, may be a little faster, but again, I'm using a 7 year old camera and its no slouch. When it comes down to it, if it takes the shot well, that's all that matters.
You will be better off saving money for better lenses, that what will give you the best quality, the body is the smaller part of the picture. Or mic, what ever floats your boat lol
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