A good handsaw and years of practice will do it. Cut it to more like 2mm or more and plane it down to your final thickness. But it’s not easy! Good luck

Only if the bread box was significantly larger.

83 years old and still kicking ass! But retired ass these days.

Snakes do not abide by the laws of nature.

Practice time! Good luck dude

Do you have a circular saw? You can do the dadoes in the sides with that by setting up a guide and taking multiple passes. Use a chisel to clean up the base afterward and it’ll be great. For repeatable assembly, maybe go for those threaded inserts combined with hex bolts.

If you search for “knockdown bookshelf” you’ll find tons of options. But my preferred way would be:

1. Vertical sides with a dado for each shelf. The top shelf should be set a few inches below the top of the side boards. Use the extra height on the sides for decoration.

2. For the top and bottom shelves (and if you’re doing it tall, maybe also the middle shelf), in addition to the dadoes, make a pair of wide through mortises.

3. The top and bottom shelves get extra long tenons to go through the mortises. They should stick out enough to put a tusk or wedge on the outside.

4. Put all your shelves in, stick the wedges in the tenons, and enjoy your rock solid bookshelf.

Generally speaking, putting the full weight of a shelf onto any screws is a dangerous idea. Screws tend to fall immediately and completely, and that’ll take the whole shelf with it. If you prefer to go screws, still a good idea to add dadoes into your side pieces to hold the weight, and use the screws to hold the sides in place.

More important than the screws is the furniture you’re building. Is it a bed? Table? Giant Victorian highboy with a bajillion drawers? The knock-down needs for all of those are different.

So uh… What are you making?