I wouldn't worry too much about soil amendments. Bamboo is a bottom
feeder, it will do well in a wide variety of soils. If grass will grow
on in, so will bamboo. I would add fertilizers once it was
established.

As for water, I live in a (normally) pretty arid climate. I water my
bamboos 3x a day for 10 mins (30 total) on a drip/mister system. It
*really* is more than is needed. I've dug to plant some other plants
that are some distance from the boos and the soil is moist pretty far
down.

As for stakes, if the plants are tall enough to be whipped by the wind,
you may wish to stake them, if wind really isn't an issue where you
are, I'd save the trouble.

Good luck!

Chris
Chino,CA (30 miles east of Los Angeles)