In some areas you can buy the pressure treated stringers already cut. I
was lucky that the precut worked for me I guess.

I take it you are trying to avoid the tedium of laying out the stairs
with a square..

You could nail the treads in from the side in addition to laying them on
support blocks if you wished to have some extra support. You can use
galvanized ring shank nails which would hold pretty well. I used some
galvanized ring shanks in an air nailer for my back deck and it seems to
have worked well. And the air nailer was pretty fast.

Ron T