It doesn't take a rocket scientist to build a live steamer. After all, the people that originally designed and built steam locos were little more than high-tech blacksmiths.
OK, you need a fair amount of machinery (lathe, mill, sheet metal working etc) tools and a lot of time. Designing and building the boiler should not be done by someone unfamiliar with the requirements therein, but beyond that, it is not past the skills one learns at a vo-tech school (or used to be able to learn).
I started that particular project in 1984 and worked on it piecemeal for 26 years to completion.
One should never rush hobbies, or they become 'work'.
Once I had the boiler on it, I though "whew, almost done"....wrong.
Piping, sheet metal and painting took another 2 years, and my loco is nowhere near what anyone in the hobby would call 'detailed'.
I will probably add some 'detail' to it from time to time over the next few years, but in reality, I have other locos that I need to get moving on. There are 3 in my basement in need of repair / completion before I start a new one.