How to copy/replicate/sync the sequences between two oracle databases

A combination of UltraCommits statements and a database link, in addition to a stored procedure that you can schedule to automatically run, would serve you well. and its a easiest way to keep this in sync.

--drop create db_link
DROP DATABASE LINK SOURCE_DB;

CREATE DATABASE LINK "SOURCE_DB"
  CONNECT TO USER IDENTIFIED BY password USING 'SOURCE_DB';

 --drop create sequences 
  DROP sequence target_seq;
CREATE sequence target_seq start with 6;

  --the next two lines run in source db
  DROP sequence source_seq;
CREATE sequence source_seq start with 6000;

--take a look at the sequences to get an idea of what to expect
SELECT source_schema.source_seq.nextval@SOURCE_DB source_seq,
  target_seq.nextval target_seq
FROM dual; 

--create procedure to reset target sequence that you can schedule to automatically run
CREATE OR REPLACE
PROCEDURE reset_sequence
AS
  l_source_sequence pls_integer;
  l_target_sequence pls_integer;
  l_sql VARCHAR2(100);
BEGIN
  SELECT source_schema.source_seq.nextval@SOURCE_DB,
    target_seq.nextval
  INTO l_source_sequence,
    l_target_sequence
  FROM dual;
  l_sql := 'alter sequence target_seq increment by '||to_number(l_source_sequence-l_target_sequence);
  EXECUTE immediate l_sql;
  SELECT target_seq.nextval INTO l_target_sequence FROM dual;
  l_sql := 'alter sequence target_seq increment by 1';
  EXECUTE immediate l_sql;
  COMMIT;
END reset_sequence;
/

--execute procedure to test it out
EXECUTE reset_sequence;

--review results; should be the same
SELECT source_schema.source_seq.nextval@SOURCE_DB, target_seq.nextval FROM dual;

How to find a Schema size in Oracle

SELECT sum(bytes) / (1024 * 1024 * 1024) size_in_gb
  FROM dba_segments
 WHERE owner = 'SCHEMA_NAME';