I took two 2-week classes at United Bicycle Institute in Ashland, Oregon: (1) steel brazing bicycle framebuilding and (2) TIG steel bicycle framebuilding.
In each class, they walk through designing a bicycle frame, we do that for one frame that we design, and then we build the frame that we designed.
For the steel-brazed frame, they teach you steel brazing in the class. For the TIG frame, the school recommends prior TIG experience or taking a 2-day TIG class always offered the weekend right before the 2 week TIG framebuilding class (I chose both).
I have about 95 videos that I took in the classes. They are uploaded to YouTube, but currently they are private videos (the school’s idea in order to let me film so much in class). I can probably make the videos public now because UBI (that school) no longer offers framebuilding classes due to COVID-19 (the instructor left during the pandemic in order to become an RN).
One data point: if you know how to do it, plan 40 hours of design, fab & welding for one frame.
You would also probably need a chainstay fixture as well as a bike frame fixture.
A milling machine is helpful for the tube mitering, but one can do this by hand.