Most screen-only protectors have no problem with the above, cept for 'glare' issue you need to get the matte finish at a slight loss of clarity.
(Forward) cam, proximity and light sensor needs no special holes cause they'll work just fine with yet another layer of transparent protector over them.

I just hope the top of N900's face plate is completely flat, so's to make application easier and better durability for the sticker.

As for the rest of the device, I'll apply invisible shield\bodyguardz-type (die-cut 3M sheets) to protect them from scratches. With them on, I can even pocket the device along with my house keys..