Should I upgrade from D3300 to D7000

Hello Reddit,

I am a hobby photographer and just bought my first non-kit lens, the nikon 50 mm prime lens and I love it. To my surprise, the lens would not auto focus. After just a short amount of research, I found the problem, no in camera motor. So I found that the d7000 has the motor and if I sell my nearly new D3300, I wouldn't have much out of pocket expense for the upgrade.

Here are my concerns:

1. I am worried about low light photography and how the 3300 will compare to the 7000 with iso settings.
2. Are the megapixels a big deal? Going from 24Mp to 16Mp seems like a big jump but will it matter if I'm not blowing my photos up?
3. processing speed and overall quality. I am concerned that my 3300, which is already pretty slow at processing long exposure photos may be better than the 7000 but I can't find any info on this.

Any help and advice is welcome. Thanks Reddit.