I’m thinking of making something similar to these stackable shelves. But I want to do it using hand tools only so it seems plywood is out of the question (searching online said it would damage my Japanese hand saw). So I’m looking at solid wood instead and getting pine hobby boards that I won’t have to plane seems to be the easiest and cheapest alternative. The shelves will mostly hold records and books and the largest will probably be 30x30x75cm but stacked on other shelves. Am I in for a bad time?
Seems to me like board width would be the main concern. Hard (for me) to get solid boards any more than 30cm/12" wide, and a shelf stack that shallow will get kind of unstable when stacked more than a few units high. Strength wise, it ought to be fine.
I think I’d still use plywood for the back/bottoms, assuming you’ll fit them in a dado, which will hide any splintering at the edges.