I have a Nex 5N and 18-55. Until today I still think is the the best "value for money" mirrorless combo, it is giving ur APS-C image quality on such a small form factor. On my last trip I ask my mum to take it for his shoot. You know old people are noob on camera and they don't even understand how to half press to pre focus or things like focus and recompose. So everything have to be auto. The pictures come back all sharp without misfocus (as long as the subject is not at the corner/border when the background will be in focus). Old people also like to print and the prints are just amazing and have all the SLR look. [I am referring to image quality, nor artistic value, lol]

When you use 18-55 at 18mm, you can use f3.5. If you buy 19mm, you can use f2.8. The difference is only 2/3 step, other than smaller size, there is really not much benefit.

If you buy the 30mm, it is effectively a 45mm view on Full Frame camera. That is quite an interesting view. And if you shoot 30mm with 18-55 you probably are now at f4 something which means now this lens can really give you more than 1 stop advantage in both low light and bokeh (background blur). So this look more interesting. But for me, it is still not interesting enough.

The 50mm is very interesting. It can shoot wide open and still get very sharp results [but not on Nex 7 which the megapixels outresolved the lens capability]. The 1.8 will give very good bokeh when needed and quite a good low light performer compare to the sigmas. It will be a good match for 18-55 because the 50 of 18-55 will need to be shot at near f5.6, you can getting 3 stop advantage! Also while not related, the silver lens look more cool then the black sigmas.

Please don't sell the 18-55, you can't get much for selling it and it is really value for the money.