Just my very limited 2c on the subject.
I'm also very new to model engineering. I had nothing 3 years ago, so all my purchases are recent, and on a budget.
You say you have a miniature steam engine to build. Do you want the bolts to look to scale? Do you have any other projects in mind after this one?
I think for anyone getting started, it doesn't matter what you decide, you'll probably spend your first few years constantly needing just one more tap/die to complete a project.
That said, unless you are doing very specific work, most threads will be physically strong enough for most applications, so the major diameters and the stud/bolt size will be the thing that makes a model look "right". How many turns you have to do to get there (TPI) is mostly irrelevant and mostly hidden once the model is built.
I'm in the UK/Ireland. Here we are well serviced, like others have said. I assume you are equally well serviced in the USA? Your profile says TX? The internet also allows you to get pretty much anything if you know the right places to look!
Personally, I went with BA and ME threads. I bought full sets of their HSS taps and dies from Tracy Tools, here in the UK. No affiliation, YMMV, but I've found them to be quick, reliable and friendly! They also have stands at a lot of the model shows here and the prices are very reasonable too, and they're pretty local so have good delivery times.
I picked BA because most of the models here use that thread size for the structural parts to the models, (Bolting to the base, bolting parts together etc) and it looks to scale.
I also use ME threads because a lot of the kits and suppliers here use these for pipe fittings and valves, off the shelf parts, etc - Anything connecting boiler bushings, valves, pipe joints and tees, etc seems to mostly be ME threads.
Those two sets worked for about 85-90% of all the work I've wanted to do, and covered all the mini steam models I've built. Total cost ~ £180.
Other things I've needed are a few 26tpi taps of differing sizes, as I recently acquired a 7 1/4 steam loco, and some of the safety valves use the slightly thicker thread.
Now, I've also done some work on newer things. I made a few fountain pens etc, and many of them use obscure metric threads, like M9 0.75 pitch.
Like others have said, get good quality tools when you buy. Be careful with them, and always use cutting fluid where recommended. I went in dry a few times and regretted it very quickly!
So, in short, look at the types of off the shelf items you will be using for your model builds, and when you buy, buy a full set.
I hope that this is at least some help.
I did a very brief bit of research, and from what I can see, thread sizes in the USA seem a bit messed up for model engineering. Here in the UK, there seems to be a lot less variance!
For example, this uses ME threads : Displacement Lubricator - PM Research (pmmodelengines.com)
but then these uses a whole range of threads: Globe Valves - PM Research (pmmodelengines.com)
Boiler Feed Pump - PM Research (pmmodelengines.com)