the reason for conflicting info is that there is no set standard, most say a foot off the ground but lower than thier roost(they tend to want to roost as high as possible) so they dont roost in nest box
some have had success with boxes on the ground
Most books recommend 1 box for each 5 hens, but you can have more boxes and all seven may use the same one. I would risk having too many rather than not enough.
I think chickens will adjust to whatever you give them.
Also you can use whatever you want in the nest box as bedding, some will say it should be straw some insist on woodshaving, some say paper, so like most things, whatever you have available will probably work, and what works for mine may not work for you, most things are juss guidelines or sudjestions, Their is no right or wrong, just a what has worked for the person answering.