Risk of bundling multiple db changes together when switching to ArchiveLog Mode and approach to rest

Source Production DB running in NOARCHIVELOG in Oracle 10GR2 has never been backed up.

1. Completed schema level expdp of all schemas except SYS in Source DB

2. Planning to switch over Source DB to ArchiveLog Mode and increase DB_FILES parameter from 300 to 500.

    ALTER  system set db_files=500 scope=both;

   

 ALTER SYSTEM SET log_archive_dest_1='location=/u01/oradata/MYSID/archive/' SCOPE=both;
 ALTER SYSTEM SET log_archive_format='arch_%t_%s_%r.arc' SCOPE=both;

     SHUTDOWN IMMEDIATE;
     STARTUP MOUNT;
     ALTER DATABASE ARCHIVELOG;
     ALTER DATABASE OPEN;

3. In unlikely event of database is unable to start up and as a last resort is the following approach a feasible way to