I collect ancient coins so I set up a macro rig, though I use the camera for a lot besides that.
I use axial lighting for coin photography sometimes, other times various diffused light from the sides, and then a ring light at other times. Overall I find the ring light tends to be best, but sometimes other approaches work. It's one of those things where for a given piece there's a lot of different fiddly things to try that come out a little differently for each coin. Metal surfaces can be tricky to photograph.
I shoot with a D5100 with either the kit lens or a 35 prime with extension tubes. I have a Sigma 105mm macro that's great but for coins it's overkill. It's really for bugs.
I'd guess probably a D3200 would be fine for your needs, just make sure that you can adjust all the manual settings you'll want. With coins the autofocus systems tend to be poorly equipped at choosing the right focal point, so the lack of built-in motor might not be an issue - autofocus only gets you in the ballpark and I almost always end up shifting to manual. So a Sigma 50 might still work, depending on how comfortable you are with manual focus.
The one thing that's a pain with the kit lens is that if you use it with a Ring light, the whole ring rotates, which makes focusing... odd.
Last edited by fisheye; 09-10-2013 at 04:29 AM.
Reason: fix typo, added a little more on AF