physical model data types

Question

I'm trying to convert a logical model to a physical model and I saw an example here http://www.1keydata.com/datawarehousing/data-modeling-levels.html which doesn't have null or not null. Next to the data types, does null or not null need to be in a physical model ?...Also I see a lot VARCHAR2(30) in the models, I know it depends on a situation of course but when would you have VARCHAR2(50) ? would you want it when you have a column something like description, location or street address ?