An old adage of ship models is to build from the bottom up, and from the inside out.
I generally find that it is easiest to paint the steel decks first, and then mask those flat surfaces off and paint the verticals. Exceptions do exist, say a smaller gun tub. There, it might be easier to paint the whole part the vertical color and then paint the small area of deck with a fine brush. Esp. if theres then a gun, direction finder or radar sitting in it.
I'm not at all sure what all of the decks are painted currently on the Whisky. It's always difficult with museum ships, which often follows after what is available via donations. Looking at a number of photos of the Iowas in the 1980s, the decks that are not natural wood are a dark gray non-skid. The verticals are Haze Gray.
They are pretty looking for sure.
Don't be tricked by the AM advertising. They love to add all that brass on unpainted plastic because it looks much more striking than when camouflaged.