I will agree with most of the folks (and hence my comment on insurance companies) - running a boiler is "non trivial". The leftovers from that era are operating engineering laws and unions

A high pressure boiler is a bomb, just waiting to go off (the one in your basement if you have steam heat is LOW pressure, maybe a couple of pounds)

Most states require boiler stamps, etc for a reason. There are usually exemtions for "small" boilers (usually under 5hp) and /or certain boiler capacities

That said, even though most of the folks in the live steam hobby are running boilers that would be exempt, and we COULD make out own, we tend to farm that part of the job out to licensed boiler makers. We also tend to spend the YEARS we take to build our own engine learning to run/fire other peoples engines

Just remember, if you do get a boiler. Running out of FUEL is no big deal, the engine stops. Running out of WATER is a HUGE deal. Look up the term "boiler explosion"