According to the Official Rules set forth by the JPBPA, each team is allowed to have 70 players on their rosters (Rule 60 & 79).  However, there is an exception to this rule: if there is an emergency situation (team mergers, bankruptcies), teams may be allowed to carry up to 80 players (Rule 57.2).

Of the 70 players allowed on the roster, only 28 are allowed on the active roster (Rule 81). And of these 28 players on the active roster, each team is allowed up to 4 foreign players, provided there are no more than 3 foreign pitchers or foreign position players at once (Rule 82.2).

Further, each team can have 1 manager and up to 10 coaches (Rule 80).