1) When a plsql block fails, you are always told which line the failure occurred on, eg

SQL> create or replace procedure bad_proc is
  2    x int;
  3  begin
  4    select 1 into x from dual;
  5
  6    select 2 into x from dual;
  7
  8    select 3 into x from dual;
  9
 10    select 4/0 into x from dual;
 11
 12    select 5 into x from dual;
 13
 14    select 6 into x from dual;
 15  end;
 16  /

Procedure created.

SQL>
SQL>
SQL> exec bad_proc
BEGIN bad_proc; END;

*
ERROR at line 1:
ORA-01476: divisor is equal to zero
ORA-06512: at "MCDONAC.BAD_PROC", line 10
ORA-06512: at line 1

If you had an exception handler, then UTL_CALL_STACK and DBMS_UTILITY can be used to get this info as well, eg

SQL> create or replace procedure bad_proc is
  2    x int;
  3  begin
  4    select 1 into x from dual;
  5
  6    select 2 into x from dual;
  7
  8    select 3 into x from dual;
  9
 10    select 4/0 into x from dual;
 11
 12    select 5 into x from dual;
 13
 14    select 6 into x from dual;
 15  exception
 16    when zero_divide then
 17       dbms_output.put_line('HELP - I DIED HERE=>'||dbms_utility.format_error_backtrace );
 18  end;
 19  /

Procedure created.

SQL>
SQL> set serverout on
SQL> exec bad_proc
HELP - I DIED HERE=>ORA-06512: at "MCDONAC.BAD_PROC", line 10


PL/SQL procedure successfully completed.

And here is some more information about handling errors in PLSQL

http://stevenfeuersteinonplsql.blogspot.com/2016/03/nine-good-to-knows-about-plsql-error.html

2) If you are inserting millions of rows, then ideally you are doing this with a single INSERT-SELECT, because that will be the most efficient. In that instance, you can typically monitor v$session_longops to see the progress.

Some examples of that here

https://asktom.oracle.com/pls/asktom/asktom.search?tag=vsession-longops-200011

If you have *code* that is doing the inserts, then you can instrument the code with DBMS_APPLICATION_INFO which can be monitored from other sessions. Search this site for DBMS_APPLICATION_INFO for many many examples of doing this.