I basically followed the same process as @Grayson_Morris - Laid a piece of construction paper down then and then poked out the holes with a pencil. Used that as a stencil to drill the holes out. (Hit 9 out of 10 perfectly and I would not waste time with the rivnuts, cross nuts, whatever they are. I think they are overrated.) Nuts and bolts were fine albiet a pain in the rear to get to the back put the not on without small hands. We then used three 2x3’s as studs to build the floating platform. Then 1x4’s for the slats. I think it is 13 1x4’s 2.5 inches apart for a full bed and a few more if the are 1x3’s and 2 inches apart. We lost a little space as our walls from are flush with the studs. I’m ~5’ 9" on the shorter side and can still stretch out with a pillow but that is the absolute limit. Slats are important over a flat surface, don’t over look them.
Ours did bend a little originally. Since then we added 2 peices of 1x6 hardwood boards on the oursides to finish the look of the bed as to not have the 2x3’s showing. That added a considerable about of strength.
On another note, I have seen a lot of people cover the back lower half of each side with 3/4 ply and attach it to the top there.