1) If I am doing ghusl and while washing the the head & neck with the intention of ghusl & there is some dirt on my face which gets fully washed off by the running water pouring on my face from the shower, is this okay? or is it obligatory for me to remove this bit of dirt before I start the ghusl? In basic terms if this dirt is removed during the ghusl, is it sufficient?

2) Sometimes I get a small amount of dandruff(dried/dead skin of the scalp). Does this affect the validity of my ghusl? I don’t visibly see the dead skin on my scalp. I only notice it when I scrub my head hard with a hair brush

1) Yes your ghusl is correct and in order.

2) Ghusl is valid and in order