1) How to correctly define a Calendar with Adjusting Period?

Usually 13th period is marked as adjusting. The period will consist of only 1 day: 31-DEC. Some companies keep 2 adjusting periods.

2) Will the Quarter be 4 or 5?

4th

3) Will the Month Number be 12 or 13?

13

4) A Calendar with a name like “Try Calendar” cause a problem when trying to save the Calendar definition? In this case, is “Calendar” a Oracle Reserved Word which we shouldn’t use?

Could be a bug ... Need more info like error message

5) What was I doing wrong for not being able to save the above calendar, with different combinations for the last row, such as the above separate two rows?

Dont know. Need more info.

6) When calendar is defined compiled and validated, it can be attached to a Ledger. When the periods within the calendar a running out, do we have to append extra periods to this calendar in question, or do we have to create another fresh calendar and attach it to the Ledger.

Append extra periods to this calendar.

7) In case we have to append perioad to the existing calendar, does it has to be a full 12 periods all the time?

One full year should be added. However you can add few months as well. (Budgeting will not work)