> 5G technology is effective only over short distance

This is not really true. Yes, the signal range is reduced at higher frequencies used by 5G (>5 GHz), but this is mitigated by using beam-forming to concentrate output power where it's needed. This means that with same output power you get very similar range on high frequencies compared to low frequencies without beam forming.

There will be increased number of cells due to smart vehicles and IoT, not due to 5G technology.

I don't know anything about health effects, though. I belive mmWave won't be built into mobile phones for some time, it's currently needed for high-bandwidth connections towards buildings, vehicles and portable hotspots.