As you mentioned whitenning would only get you one shade whiter on our scale. Porcelain veneers on the other hand would give you the color you want permanently. Your case in particular need a protective guard and retainer and can be helped with boutulin shots for bruxism
The type and brands of porcelain is key and last but not least the type of cement used to bond the veneers along witht the design and thickness of each veneer. Once the veneer is bonded there is prety much nothing you can do to change.
There are tools that messure teeth and programs to design digitally to obtain better results. Veneers are very thin shells of porcelain and they can have different shapes, shades of colors, textures to help the design look more natural.
A porcelain veneer cannot be reglazed in the mouth. It needs to be done in a lab with an oven. Special tools are used to recover and or polish veneers.
The root canals are done on the back of the tooth. Veneers dontcover the tooth on the back. The cavitie or hole is sealed with resin once the root canal is performed. On the other hand crown veneers do cover the entire tooth. and the endodontic doctor will seal off the cavitie he does on your crown veneer just like he would for your natural tooth. If a veneer brakes we need to do an impression and redo the veneer.