Hate the look of the halos, might stop a large object but not a bolt or spring falling from a car, even a danger that the halo can divert it into the body. As far as driver ID I think one of the cars cameras is bright yellow.
Yes - the one for whichever driver has the higher race number. For example, Ocon has one at the moment because is 31 is bigger than Perez's 11, but if he went to Mercedes next year and either of its current drivers (Hamilton 44 and Bottas 77) stays, he'd lose the yellow camera bar to whoever at Mercedes stayed on.
In practise, some of the number-driver associations have not stuck well enough for me to be able to use that method in the heat of battle, and neither of my parents can do it at all (Dad can remember Riccardo, Vettel, Hamilton and the Force India duo because he remembers from the season preview and me telling him; Mum cannot do any of the race numbers at all because she likes to rely on the screen and the new font is poor).