Outlook has thousands more features that Outlook Express and is typically
used in most business environments. To ask any of your questions depends on
what your needs are? I wouldn't buy Outlook just because other people said I
should.

Your wife can use Outlook Express as well. There are essentially two ways
you can set this up - (i) where you both share the same mailbox; or (ii)
where each of you have a totally independent mailbox.

To use independent mailboxes you would create a new Identity for your wife
(File/Identities/Add New Identity) and use File/Switch Identity to swap
between your Identity and your wife's Identity. You may also want to turn
off the option "Use this Identity when starting" under
File/Identities/Manage Identities which will make Outlook Express ask you
each time it starts which Identity you wish to open.

To add your wife's email account details under either option select
Tools/Accounts/Add/Mail