You recall incorrectly about the thickness but yes, steel is heavy.
SPCC Hot rolled coil_Shandong Bailiyuan Metal Manufacturing Co., Ltd. (blymetal.com)
Is anything stable indefinitely? It has not been my experience that comes off easily. Indoors, on a wall, occasional wiped with Sonax or whatnot it would be fine, if one wanted the industrial look.
That's what I would call no-spangle and it also stains. Low spangle looks something like silver hammer-tone paint, and it does not stain as easily. High-spangle looks like what people usually think of when they hear galvanized. I think this would be ideal as it wont chip, rust or stain. You can write on it with a marker and it cleans right off with acetone.
The bummer about paint is not only that it chips and wears off, but that markers and whatnot will stain it.
The only thing you have to be careful of with galvanized is white rust, but this would be visible by the time the OP got it.