Lots of very good questions and comments here.
Hopefully, I can live up to the standard.
I own the 35mm 1.8G DX and it is a very good lens. That's my personal opinion and I have yet to find a review that disagrees. There are sharper 35mm lenses, but they are 4 or 5 times the cost.
I was recently looking to purchase a 50mm prime. I went with the 1.8D (which can autofocus with my body, but not with the 5200). Several people have compared the 50mm 1.8G to the 50mm 1.4G. Their conclusion was that the 1.4G had some advantages, but the 1.8G could actually provide sharper images than the 1.4 at some apertures.
I have no affiliation with this, but it helped me when making my decision:
http://photographylife.com/nikon-50mm-f1-8g-vs-f1-4g
The man that runs the site is very meticulous and much pickier than I am (I mean that as a compliment). So my attitude is "if it is good enough to make him happy, then I won't be disappointed."
Personally, between the 35mm 1.8G, the 50mm 1.8G and the 50mm 1.4g, I don't think you'll see a much of a difference in image quality. So many other things (lighting, iso, shutter speed, camera vibration, filters, white balance, etc) will have a larger impact on sharpness and bokeh.
Good question, and a personal one. I have seen many online fora conversations get quite heated on comparing the merits of say, the 85 f/1.8 vs. the 85 f/1.4 "Cream Machine". I have no personal experience with an f/1.4. I know that FOR ME, my money was better spent on getting both a 50mm f/1.8 and 35mm f/1.8 versus just the 50 f/1.4.
You could get a 50mm f/1.8D (old one with aperture ring) from KEH, a good reputable used equipment dealer, and save a little money that way. If you find you like the focal length, you could sell it back to them, take a bit of a hit, and then go for the f/1.4. However, the 50mm f/1.8D can be found for right around $100 new. The 50mm f/1.4D can be found for $100 more. It's not like buying a 70-200 f/2.8!
But keep in mind that you will have to manual focus with these lenses because the D5200 does not have an autofocus motor. You'll need the 1.8G or 1.4G if you want to autofocus.
+1 (again, a personal question, but this is where I came out, as well).
Image
50mm 1.8 on a DX camera at f/10. Note that this is a really old example, the Series E pancake. Even the midget nifty-fifty is plenty sharp, has good bokeh and a good focal length for portrait work (on a DX camera, at least; I think the crop factor puts it at about 75mm or so). Unless you're working in very dark/fast settings, save your money and get the 1.8.
i highly doubt iil do this but if i had a full frame id be set on a 50mm. maybe i should return the d5200 and blow another grand on the nikon d600? Lol