Very little has changed about building a steel frame in the 40 years I have been building bike frames. And really, there is not much different between those frames and the oldest ones that I have seen. Sure, there are better tubes now and you can't cold set a lot of them. So mitering and construction has to be done more carefully. That's not much of a change.

Bike tubes are cheaper than any other kind of tubing that would work for a bicycle frame. So you might as well start with the cheapest bike tubes you can find.