As has been pointed out, this is referencing the Periodic table... but the other answers got the references backwards.
The answer is
Ash
Add to me one and I'll become a mess;
1 on the periodic table is Hydrogen, H. H+ash = Hash, a synonym for mess.
Add to me six and I'll buy you a dress.
6 on the periodic table is Carbon, C. C+ash = Cash, something you buy a dress with.
Add thirty-five, I'll get bolder and louder;
35 on the periodic table is Bromine, Br. Br+ash = Brash, a synonym for "bold" and "loud".
Add to me none, and I'm left as a powder.
This one is more literal, as Ash is a powder.