I have had a 5100 for about 18 months, and it is my first dslr camera. I used point and shoots before that, and have always enjoyed taking pictures. This dlsr "hobby" is expensive. You will want more of everything soon. Lens. Software. Accessories. NAS is used to describe what all the members of this forum "suffer" with. (Nikon Acquisition Syndrome) Some are in the later stages, some in the early stages, a few are in denial. Those of you in Egypt, you know who you are...
If I had the choice today of either a 3200 or a 5100, I would buy a 3200. (If I couldn't wait for the 5200) I like new rather than used for the warranty.
Why 3200? Simple. The sensor. (24.2 vs 16.2) and a little faster processor.
I have heard it said that the size of the sensor does not matter, and that 12 MP is plenty. I also note that these photographers are shooting the newest mega pixel sensors, mostly. Size matters.
Ability to shoot bracketed photos (5100) is nice, but not a necessity. If you think you will want to shoot using HDR for post processing, then the 5100 would be the choice. Photomatix will do a pretty good imitation HDR with only one shot. (Probably not the way to describe that...) Post Processing (PP) will play a big role in your hobby...
Yes, there are other differences. For instance, I have never used my 5100 for video. Never used the swivel LCD, other than to play with it. I use the viewfinder. If I wanted a video camera, I would go get one.
Again, I will state that I am very new to this hobby, and perhaps future experience will cause me to change my mind about things. This is only my *opinion* at this point.
Whichever you choose, you are getting a very good piece of equipment. As will be pointed out, the lens you use will make a huge difference, and, of course, this is where NAS starts getting worse...
Good luck, and good shooting!
Carroll