Should I trade my lens?

Should I try to trade my Sigma 70-300mm f4-5.6 for a Nikkor 35mm f/1.8? Leaving me with a 35mm and a kit lens?

At the moment I'm saving up for an apartment (so I'm not trying to spend much) and only plan on doing a few portrait jobs on the side.

Well, the 70-300 is slow and that is not good for portraits, its not a good lens anyway. The 35 is fast, but too wide for portraits, great lens though. Consider an 85mm f/1.8, its fast and is a portrait lens.

You should be able to make your own decisions rather than rely on the internet.