What is the correct syntax to create tom/dick/harry objects all in a single .pl file and then use them?

Being Perl there is no "correct" way - TIMTOWTDI and all that :-) That said I tend to always write inline classes like this:

{   package Foo;
    sub new { bless {}, shift }
    # ... other methods
}

{   package Bar;
    use base 'Foo';
    # Bar specific methods
}
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Sticking each package in its own { block } means I don't have to worry about lexical variables leaking between packages, and using use base rather than assigning to @ISA directly means I don't have to add extra use BaseClass lines if I decide to move it to a separate file.