Memory requirement (for HDD) for Android based tablet?
This is really an "it depends" answer. If you are only installing applications and streaming any media you consume, 16GB is sufficient. If you are copying media locally, 32GB should be a minimum.

By way of example, the tablet I was using on my last vacation only had 2GB used. My son's was full at 16GB with the movies and TV shows we'd copied on to last him a week and he ended up watching the same shows over and over.