I live down the road from Kennedy Space Center, and it has a fairly large scale :). It is also quite commercial, or rather the 'theme park' part of it is. By scaling, I presume you mean to spread, similar to a franchise model. Or do you mean a single park which grows really big? A little more detail about your vision might help.
Most of these kind of places have either a 'draw' or a 'museum' model. Ones which have a draw have something which is not elsewhere, which is what draws people to go there. KSC for example has rocket launches and moonshot facilities which are quite unique. A museum on the other hand can be built anywhere, even though it may contain some unique things. For STEAM it doesn't need uniqueness, just cool stuff would do. An example of that type would be www.mosi.org.
Museums are great, but in our day and age, building one is usually not a way to get rich. They often have some kind of subsidy. I don't know a ton about their finances, but most are operated as non-profits. I'm sure you could talk to someone who runs one and they'd be happy to tell you about their costs.
Having a STEAM draw might be good, but probably won't scale in a franchise fashion. However, linking up with a science institution can lend prestige, which is really important in the education/kids market. If SpaceX were to open a STEAM-themed kindergarten, parents would be fighting to get their kids in. Of course, this can also be done poorly - Florida Tech should have the prestige of being basically 'NASA school', but instead you get the grey MBA-ness of https://www.fit.edu/education-centers/locations/spaceport-ti....
The most important thing to find out if you want to scale, is what is the cost structure for existing places (i.e. how much goes to rent, salaries, exhibits, marketing, etc.). Then figure out what you are doing differently that will beat the pant off that. If you can't figure that out, you can't scale. For comparison, take a look at the cost structure of those tutoring centers (like Sylvan Learning); they do scale, but they are almost certainly not what are envisioning.