Here is an easy way of looking at this problem:
I. The set of all functions mapping N to {0,1} are all of the different functions that you can imagine for mapping the Naturals to a set of 2 elements. Consider a function from N to {0,1} to be a subset of N (lets just say a subset of elements of N that map to 0). Imagining all of these subsets equates to the Power set of N which has cardinality equal to the Reals which is uncountable.
II. Here, we are dealing with functions that map {0,1} to N. This would be all of the subsets of N that have 2 elements. This in turn can be thought of as the set of all rational numbers (1/2, 1/3, 4/16, ...., etc.) The set of rational numbers is countable (there's a cool proof of this in Sipser) therefore this set is countable.
III. The largest subset of N is N itself so this is kind of trivial as it is, but any subset of a countable set is also countable. A subset is always less than or equal in size.