Reply by CplSteel

The problem with a backless bookcase is racking, it is solved by having enough shelves (cross supports) to eliminate the racking, making these shelves thick will assist in eliminating racking, also attaching a bookcase to the wall will help. Because you are going with thick shelves and attaching it to a wall, you are basically set.

You just need to figure out what you want the bookcase to look like. Once you know the look you are going for then it becomes an issue of how to achieve that look, which should not be a problem with your criteria.

FYI, 16” is a bit deep for a bookcase.