Nikon 50mm 1.8/D

I recently purchased a Nikon 50mm 1.8 D. I am still experimenting with it but would like to hear from users out there on their findings, especially on

1. With indoor, in moderate light what aperture you find the best sharpness.
2. In general, what aperture stop is good for portraits?

I thought of asking for your advice, as I don't want to reinvent the wheel. Thanks guys.

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D90, 18-105 Nikon/28-300 Tamron/50mm 1.8 Nikon