Yes, please focus on one level and the general features of the game can be left as they are in the 2DGame Kit. Though it is good to note details like health, damage, range, etc. as these are variables that can be changed easily and can be very important to the level design.
Also, for readability's sake, avoid handwritten notes. These are not your notes, this is work you present to others - so it's main point is clear, readable information. Focus on that when adding text and any other type of information into the document.