Branding

I have considered branding as an alternative to eartags....would prefer to brand using liquid nitrogen...my questions include: do you need brass branding numbers for liquid nitrogen or would the old non-brass branding irons work? what size numbers suggested for what ages? what is best age to brand? length of handle a consideration?best place on body? any and all advice invited...but please remember I will probably be using liquid nitrogen...as it is readily available....thanks in advance.