Wood, screws, glue, etc

[mdk]

I'm sure that this is somewhere, but I haven't been able to find it. Since many of us want to build "light", it's often the integrity of joining things together, angles, reinforcements, and design that brings strength, so, here's some questions that I hope someone has really good answers to.

1. What strong, solid wood holds screws best? Or, does plywood hold screws better than solid wood? ( refer to #2 for application)

2. A joint made of plywood and wood, joining two parts at right angles - is adding screws stronger than just gluing it? Assuming the wood is 2x2 and the plywood 1/4 in or thicker.

3. What wood glues to best, as well as being strong and resilient resilient (not brittle)?

A few years ago, I built a box for some metal poles and parts that was 6 x 1 x 1 ft. (just one sheet of plywood) It was made of 1/4 plywood, with all the corners reinforced with 3/4 x 3/4 solid cedar, glued and screwed. It was about 150 lbs filled, and it got dropped, slamed around in the truck, walked on, used as a bench, used as a bridge, all while both loaded and empty. I figured it to be fragile, but it turned out to be almost indestructable. Eventually, a fall to a cement slab, hitting one corner first, split a corner cedar glue block and caused the corner to open up.

What would be the best woods and do the screws help or weaken, or don't matter?