TIg welding box cutter blades can be very good practice because it makes you get used to focusing your eyes on a very small puddle, you have to get used to using a very small filler wire, and you also see how beneficial it is to use aluminum backing on thin metal.
Modifying Wrenches is common practice in certain industries like aviation maintenance. There are tight areas where a conventional wrench wont fit.
Hastelloy W is usually a great choice when you know its steel but cannot determine the exact metal type.
There is a bunch of data that states 4130 chromoly tubing .120" and under does not required a preheat or post heat treatment. But a preheat won't hurt.
This video shows tips, tricks, settings, and techniques for TIG welding 18 ga carbon steel lap joints
