That is awesome! YEARS back, a few of us were sitting around one's garage, & another made some metal flowers for his girlfriend. We then spent our exciting Saturday night chattin' & watching metal rust. (There may or may not have been adult beverages involved.) Obviously the metal didn't rust that night, so we then realized salt water should do better. Your vinegar addition worked even better!
Also to keep that rust-look, you should put some protection on it (wax or clear coat or other specialised products). If you don't do it, within a few years your fire pit will be peeling off rust and/or have more holes than it has already :) Alternative is using weathering steel (COR-TEN) if you have a bigger budget :P
I didn't really make a plan of it all. But I can tell you the sides of the triangles are 55, 47 and 47cm. The legs are also 55cm high. That's about rigth :)
