So it depends on you. I had long statements and edited them down to the boxes, with the last line being "In the attached documents I have included evidence to support the above statement" and then for each of the boxes I have a pdf with photos or bills or whatever to fulfil each category. The first page of each PDF is a 'cover letter' of what the file contains and notes which bits of the statement that photo or whatever is evidence of.
People seem to do it a number if different ways, so I don't think there is a "wrong" way (apart from not having a statement at all/providing any evidence to back it up), but I imagine a CO would appreciate you being concise and to the point.