IMO an online course will attempt to cover most everything, kind of a history of the world type coverage of gunsmithing. Too much to tell and learn and like someone else stated there's a point where you have to go hands on.
The best thing is that you don't have any expectations of this being your full time vocation at least right now and for the moment it's a hobby/interest that you'd like to pursue because of that and you have some time.
With your main interests in handguns, I'd start with a few good books like the Kuhnhausen's books. Technical, but also easy to understand. Written from the bench top attitude of fixing things instead of just telling you what the parts are called.
The 1911 has been gunsmithed to death since forever and there are countless articles and books written on accurizing, rebuilding, and customizing the pistol.
You might get in to some wood work in making grips for handguns and then checkering as you go along,,plenty of stock making books and info around too.
Then on to metal finishing,,bluing, ect,,which would require you to do your own polishing,,
It's easy to see how one interest feeds another.
Don't get all wrapped up into thinking you need to learn it all. Start with something you're comfortable with and already have a knowledge of like the handguns mentioned and dive into that.
Expensive machine tools like a lathe and mill can come later, Some basic precision hand measuring tools are good and build good skills with simple files, punches, stones, screw drivers, hammers, ect.
I've said many times, I have made a living for extended periods by doing nothing more than fixing the battered screw heads on high grade collector guns,,and it's true. But there are several skills needed just in that little specialty of fixing them up,,and I don't weld them up either.
You'll soon see which direction within there you want to go,,rebuilding worn actions,,building target guns, custom and conversions from common base guns, maybe something entirely different will strike you along the way.
But the knowledge you pick up is never lost or a waste.
Best of all, you feel no pressure to produce, no timeline, no competition as you are doing this as a hobby.
Let it go where it takes you.
Just some thoughts,,
