Referencing data in my formulas from specific file names in SharePoint.

I believe the answers are No and No.

You might want to consider making the master the data source and then pulling data from the master to the subsheets so you only have 1 data connection per sheet but you will still need both open for that data to get updated using a standard cell links like that.

Alternatively you should consider using power query (data tab and go to get data and select file and then select excel file) and then you can use a refresh data button to update the data and that should work without having to open the other sheet(s).  

In no case will you be able to link to a file that isn't created yet. (except if you use some sort of VBA code in which case you could but note that it would have to run in the desktop version to work)