Is there a way to specify the initial size of MySQL File-Per-Table Tablespaces? Preparing for massive data import into a MySQL 5.7 community instance, I'd like to know if there is a way to allocate upfront the total amount of space that will be used by the volume of information?

The purpose would by to eliminate overhead caused by the gradual auto-extend increments of the tablespace that, according to the reference guide, will be 4MB at a time, tops.
No. For ibdata files you have variable innodb_data_file_path=ibdata1:XXXXM:autoextend you can specify one or more but not for individual table spaces.