Import Oracle .dmp with error 1659, unable to allocate MINEXTENTS beyond 3 in tablespace SYSTEM
01659, 00000, "unable to allocate MINEXTENTS beyond %s in tablespace %s"
// *Cause:  Failed to find sufficient contiguous space to allocate MINEXTENTS
//          for the segment being created.
// *Action: Use ALTER TABLESPACE ADD DATAFILE to add additional space to the
//          tablespace or retry with smaller value for MINEXTENTS, NEXT or
//          PCTINCREASE



As stated above you have two options, either increase the size of your SYSTEM tablespace, which might be easier or first extract the table DDL(CONTENT=METADATA_ONLY) from the dump file and alter the DDL script to change MINEXTENT to lower value and run the script to create tables then import the data(CONTENT=DATA_ONLY).

From comment...


  I'm afraid I don't. I do have this query in my clipboard history: ALTER TABLESPACE ADD DATAFILE but don't actually know how to use it or why is the SYSTEM schema being used here when I created the IMPORT_MAN user/schema


The SYSTEM mentioned in your error is a tablespace, not a schema. SYSTEM tablespace is used to store metadata of system and user objects such as tables under SYS schema. So, while importing the tables you need to have space on SYSTEM tablespace as well as in user's default tablespace where it stores the rows. To add datafiles, refer to this link ALTER TABLESPACE