How many outlets can be wired to the load side of a GFCI?
Check the specs with the GFCI manufacturer.  

Square D for example has a few requirements for GFCI breakers.


Must be located no more than 250 ft. (76 m) from the load being served.
UL requires that
GFCIs must be operational at 85% of the rated voltage


Other than that, there is no restriction per se for how many outlets can be on one branch circuit,  residential speaking that is.