Do you want to build the Missouri as she appeared in 1944, wearing Measure 32 camouflage
USNHC Photo
or do you want to build her as she appeared in Tokyo Bay wearing Measure 22?
USNHC photo
Measure 22 is a simple matter or masking from the lowest point of the deck shear level with the horizon. Everyting above is Haze Gray (5-H). Everything below is Navy Blue (5-N).
If you want to do the Measure 32 you need to obtain a set of camouflage diagrams from the Floating Drydock and using some creative Xerography make a set of masks.
The easiest way to paint a ship is to airbrush the deck vertically (Weather Deck Blue 20B). Then go back and airbrush the bulkhead color from 45 degrees below the level of the deck - allowing the deck to mask the paint. This leaves only the bottom portion of the deck which must be hand-touched up. The alternative, demonstrated by Mike Ashey in his Basics of Ship Modeling book (good reference)is to mask the deck with millions of small tags of masking tape.
As far as aftermarket details - look at Gold Medal Models offerings.
They are very good and complete -- however for a newbie ship modeler - which you profess to be - let me suggest a less intense ship modeling experience as a first time project. I recommend the Tamiya Fletcher. Fewer parts, less expensive, less complex, less intimidating - a good learning experience