I used to have the blacked out headlight covers. IF I had to estimate I'd say they cut output 30-40%. I have 20% on my front side view mirrors and 17 on the rears. If I didn't have auxiliary backup lights I wouldn't be able to see jack when backing up unlit roads so it's probably good for another 20-30% cut in vilibility from the front in low-light night time conditions if I were to do that to the windshield. There's already some times with my side tint where on dark nights I've almost missed some stuff that would have only been visible through those windows.
You're all set on doing what you're set on doing and I'm quite sure nobody will change your minds so alls I have to say is be careful and drive slow on dark, unlit roads at night. Your forward visibility is cut by ALOT more than you probably realize, especially the guy with the windshield tint and blacked out headlights. I had my headlight blackuots on for 2 years straight and didn't think it was that bad until I took em off and looked at how much further the beams went at that poit. I would at least hope you nix those things when the sun goes down.