How would we know? How are you thinking of growing?

Kochia is an annual. You sow little brown seeds and they grow into bushes over summer then die. They make annual hedges if you so like or lots of little bushes. They tend not to look as pretty as the pic on the seed packet but are well worth the little effort they need to grow. They do self seed.

I've answered under your second question on this subject, but will just confirm that you are right, in some parts of the world, varieties of this plant can be incredibly invasive - in parts of Canada, it is now resistant to Roundup too. But it's not a problem here, as Kildermorie says, it'll be dead by midwinter.