You should try engineering with wood. Due to its inherit randomness as a natural material, you need to make a huge number of assumptions for even a basic beam. Steel and concrete design are child's play in comparison.

The US Forest Service's Forest Products Laboratory writes the bible on the subject: "Wood Handbook, Wood as an Engineering Material." It's available as 509 page hardcopy. The PDF is free to download. The current version dates to 2010. It is a great resource for anyone who works with wood, even casual builders. It helps answer a majority of the questions that Rob posted at the start of the thread.

Here's the direct link to the full PDF.
https://www.fpl.fs.fed.us/documnts/fplgtr/fpl_gtr190.pdf

Here's the book's main page with links to the 20 separate chapters.
https://www.fpl.fs.fed.us/products/publications/several_pubs.php?grouping_id=100

Here's a few of them:
Chapter 02: Characteristics and Availability of Commercially Important Woods
Chapter 03: Structure and Function of Wood
Chapter 04: Moisture Relations and Physical Properties of Wood
Chapter 06: Commercial Lumber, Round Timbers, and Ties (explains how lumber is graded)
Chapter 05: Mechanical Properties of Wood (multiple tables with specific gravity and stress values for virtually any species of commercially available wood)
Chapter 07: Stress Grades and Design Properties for Lumber, Round Timber, and Ties
Chapter 10: Adhesives with Wood Materials- Bond Formation and Performance
Chapter 12: Mechanical Properties of Wood-Based Composite Materials
Chapter 17: Use of Wood in Buildings and Bridges (here's the really fun stuff)
etc...

Here's a table of mechanical properties from the previous edition: