For white balance, is it better to adjust white balance based on the scene or set it to auto?

First option is the best. Adjust white balance based on the scene can keep a set of photos style consistent. Auto white balance will ruin the consistency of it.

Recommend range of white balance

3400-4000 for warm light settings 5000-5600 for outdoor natural light

Street portrait

Flash, white balance, dark background, bright object.

Flash: range set to 0 - 0.7 level in ttl mode.

White balance range: from 4800-5600 based on the model skin tone.

dark background: exposed level from -1 to -2.