Practice Tubing for Miters, Tig and pretend Lugs

I want to practice mitering with a hacksaw and file and then, after passing my Beginning Tig Welding final (a variety of welds on flat pieces), take the mitered sections to school and try welding them together. To make the most of my material, I thought I should get wall thicknesses that play nicely together such that I could then take these practice tig pieces home, carve them some, and pretend they are lugs to practice brazing. Does that make any sense? Will the 4130 that I get from Aircraft Spruce behave in the slightest like a lug? If so, how thick should the "lugs" be to play the part and how much play should I aim for between the tubes for brazing?

Do a google search for "slip fit" and "practice lug material". My bit of advice would be to separate the two. Practice welding, and practice sweating joints; but at this point don't worry about trying to weld practice lugs. You have enough new skills you are working on that I'd think it best for you to compartmentalize until they are not fresh tasks.