When producing a list of available parameter properties, rather than manually typing each persons name in one by one, is there any way of just populating the data from the table/view which holds all the possible names?
I assume its in the circled box however all that does it let me point to a dataset and then field which I have tried selecting StaffName (being the field that is the one I’m using) if I then run the report it falls over.

SSRS’s concept of a query is largely tied to a data set that you define in Report Data.
When you choose ‘Use a query’, you should be choosing a pre-defined query from Report Data. Of course, the good news is that you can define these yourself.
So let’s take your example. You want your possible parameter options to be StaffNames.
Create a new dataset in Report Data. It should return all possible staff names for your report.
Once you have defined this dataset, you should be able to use it as a source of parameter values.