index question

Hi - I have a question regarding an innodb table we have that currently has 6 indexes which, for ease-of-use and brevity, I’ll display as:

I1: ABCDE
I2: ABFCDE
I3: GBFE
I4: ABFHE
I5: ABFCE
I6: ABCE

All indexes are non-unique.

Given this series of indexes, wouldn’t I1, I5, and I6 be unnecessary?

Would it be better to replace the indexes with a single index (A-H)?

Is a non-unique index of N columns better/faster than N indexes?

This table has slightly more than 3 million records and records are periodically updated.

Thanks!

I2: ABDCDE – D twice?

-no
-no
-depends on the query