But 73,000 characters is too big for a trigger really. Trigger code should be kept as short as possible, with most of the logic performed in a packaged procedure called from the trigger. That will be more efficient, since SQL in triggers gets parsed each time invoked, whereas in packages it is cached. See this link for details.
Triggers are stored in the data dictionary, within the SYSTEM tablespace. Their names and some properties are visible through views like dba_triggers (and all_triggers and user_triggers) and additionally through views dba_objects (and all_objects and user_objects) where object_type = 'TRIGGER'.
As for their size, I had one trigger that was over 2,000 lines. At an average of 50 chars per line that's 100 KB. According to the Oracle Reference guide, the limit is imposed by the tool executing the stored procedure or trigger, and can be between 2000 and 3000 lines. It does not say how many characters or bytes this equates to, although non-stored SQL statements are limited to 64K characters.