There is not really a route from such playing to engineering except for the general kinds of reasoning involved. It's a cute idea, but does not seem very useful.
"Real" architecture and civil engineering, as done by adult professionals, deals with exact same challenges (and then some more). The work is more complex, you need to explore relevant fields of study much deeper (and professional education gives you just that, in a structured way), but it's fundamentally the same thing, just in hard mode.
Anyone who has built a personal project and a real-world professionally engineered project knows that the actual tasks involved are wildly different. What you think the correct solution is becomes a tertiary consideration. You need to consider the desires of stakeholders, money people, regulators, and quite a few others. Designing a treehouse for fun and designing a professional solution to a list of sometimes contradictory constraints and optimizations scratch some very different itches.
One is very clearly play and one is very clearly work.
You mean, like, parents? :).
I don't see the difference. The considerations you listed can sometimes dominate the object-level work, but they're also mostly generic skills for all creative white collar jobs. The core that distinguishes an architect from an aviation engineer or a graphic designer - this is the treehouse stuff.