Staff can be singular (when you refer to the whole group) or plural (when you refer to individual members of the whole group) e.g.:
The staff were very helpful .
If the staff is very large, you might want to divide them into smaller groups.
I read that in American English, staff is not used as frequently as in British English, and is never followed by a plural verb. Perhaps somebody speaking AmE could say what they think.
Also, you don't refer to a person as 'a staff' but as 'a member of staff'.
As far as much more is concerned, I think the form has something to do with the fact that this 'more' hasn't been defined. It's like a promise that there's more to come but we don't know what it is exactly, so it's treated as something undefined and so - non-count.