nails into drywall only won't hardly hold anything. Use glue/construction adhesive as a last resort. Studs should be every 16" on center except at the ends and maybe around windows and doors. Not hard to find. Get an electronic stud finder, a cheap 2 dollar magnet stud finder at walmart, pound on the wall with your fist to find the general location, and/or push a nail through in a line along your chair rail line to find your first stud. Before you paint, write down your stud measurements on a piece of paper. Also remember for baseboards that there will be a 2by4 bottom plate all along the floor. good luck.