No amount of tint will provide privacy at night with interior lights on. If the tint was that dark, you couldn't see out in the daytime either. You need window shades for that.
Rustoleum gloss black!
Cut to fit reflectix works great, SMB shades work OK (there are gaps so you dont' get a total blackout, curtains probably don't have the gaps the shades do. I'm not a big tint fan, so I don't have any advice there.
I have the medium tint from Sportsmobile. Also the passenger and driver window was tinted through an aftermarket shop. If I had the choice I would go darker. But if your afraid of it being too dark then medium is a good choice and you won't be disappointed. People usually can't see in during the daytime unless up next to the van. It allows plenty of light in.
Due to financial limitations, I have gone with cheap "static cling" removable type of tint from walmart for the time being.
I have the darkest available 5% I think, and you have to be up next toy the window to see in at night with the lights on.
The downside is that it looks like temp tint. Many bubbles and no real way of getting them out. But this separation of the tint and glass adds to the refraction of the light and not allowing view of the interior.