Well considering that you don't seem to understand the implications of putting indexes on tables, you sure were keen on doing so, eh?

Adding more indexes slows up delete, insert , and update (on the indexed column). Rule of thumb says that if an insert takes 1 unit of time with no indexes on table, then for each (non bitmap) index added the insert will require an extra 3 units of time. Maybe a little more for function based indexes.

Also, you can easily invalidate your support contract on a 3rd party app by adding/modifying/deleting indexes.

Maximum no. of indexes per table can be found in documentation -- look in the Reference manual, under database limits.