1) "Luxurious"
2) If you always have the shade up, why get tinted?
3) Tint looks darker to someone looking in than it will when you're looking out.
4) Tint is measured by VLT (visible light transmission), therefore, 20% allows 20% of the visible light through. If that's too dark, you'd actually want more VLT, not more tint.
5) It's really up to you to decide if that'll be too much. Besides, most people looking in won't be able to see the shade if the rear window is tinted. hich leads back to the questions about why have the shade up if you're tinted (or why tint if you leave the shade up).
It all comes down to personal preference.