See if these help.
Ellen, if you have wide Enough Studs you have two options:
A. Recess a Cabinet or Several into the Wall between studs for example to make an Integrated Bookcase.
B. Go large on a Cabinet or shelving unit.
If you go too small you may end up needing an Architect sooner than you planned.
We use to use hollow wall fasteners. If using hollow wall fasteners make sure both are level. Drill hole size of outside of fastener, then there is another piece to prevent fastener from turning or spinning and screw till you cannot tighten no more if using hook on shelving or drilling shelving make sure diameter of hole is no larger than screw. Remove screw if using hangers, if using holes in shelves screw is approx. 2+ inches in length. Also check weight of shelf and what ornaments you are planning on adding then with this weight add another 10 pounds for further years down the road, you might get Pet Rocks for the shelf. That will determine size of hollow wall fasteners.
Ellen,. Where the studs fall short, you need molli bolts. They look like a small rocket. You screw them into the wall, then the back opens up against the back part of the wall, to secure the bolt. Aloha
Attach a board such as a 1" x 4" across the wall into the wall studs that you do have. Then attach vertical pieces of the same thickness behind each shelf support to make it flush.