It quickly pays for itself. Or, you can tack your pieces together with an arc welder and have a pro do the final welding. Don't be casual about welding safety, use all the right protection like gloves, boots, long pants, eye shield, etc. A MIG welder would be better and easier, and if you can get one, so much the better. Steel Square steel tubing was used where possible because it's easy to cut and fit into clean joints, easy to clamp, joints have more contact area for longer weld bead and brackets fit squarely against it.
Round tubing is stronger, but a bit harder to work.
A good metal supply store is worth searching out. My local store has stamped tabs, brackets, gussets and flanges for cheap prices, saving much cutting, drilling and grinding to make small parts. Home supply stores are pricey for steel stock, but the chain link fence supply area has some bargains in tubing and bracketry. Be sure the frame is not fancy chrome-moly tubing, since it requires a different type of welding. The headset bearings should be sound, even though most of the weight is carried by the rear wheels.