How many steps to mate the only king with all pieces? Suppose Black has only one king in its initial place and White has all 16 pieces in their initial places. How many steps does it take to ensure a checkmate? And what are all solutions?

Now that White changes his position with Black. White has only one king. Then How many steps does it take to ensure a checkmate? And what are all solutions?
Your first question: It takes 6 moves to mate the black king. 
The only move is 1.e2-e4. All other white moves would take more than 6 moves... Also after 1.e2-e4 there are a lot of variations to long to post it right here. 

The simplest way is to get the details and answer the second question yourself is using the program popeye, see http://sourceforge.net/projects/popeye-chess/

Final remark: There is a well known chess problem with white initial position and black king on h4. How to mate in 3 (white to move...)