I hung a 1'x5' mirror on the bathroom door with some mirror adhesive I bought at Home Depot. It's been there for over a month now and I'm guessing it's not coming down. I would think something along the lines of the panel adhesive your talking about or even 'liquid nail' type adhesive would work also. Just read the label for compatibility.
As far as stud spacing goes, on interior walls you can just push on the wall and feel it push in until you hit a stud then it feels solid. Exterior walls are harder to find studs. You can't use molly bolts because of the sandwich design. If I were hanging shelving on an interior wall in a closet I would use liquid nail adhesive along with some short screws to help hold till the liquid nail sets up. Like mentioned before using a larger piece of wood as a backer is also a good idea. Not sure what type of shelving you're actually installing. Some pics or a link would help in determining what kind of fastening system would work best.