What do can I do to keep the inherited naming structure and autoload the tie routines? Can I put multiple package statements/sections in my one ABC.pm file?

Yes, though it can get a little messy. For example, you could call this module

package Foo;
use strict;
use warnings;

package Foo::Bar;
use strict;
use warnings;

sub foo {
    print 'foo';
}

return 1;
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with the script

use Foo;
use strict;
use warnings;

Foo::Bar->foo;
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Note that you cannot use Foo::Bar since the file does not exist. The Foo use statement loads Foo::Bar into the namespace. (-- Not quite true: see below)

52 of them make autoloading seem worthwhile. Although if they are in separate packages, each one containing only the tie routines for one "tie-to" name, maybe autoloading isn't worthwhile?

You can use a base class (i.e. ISA) to define your autoload routines, so no matter how many files you have, the actual code is localized. A good intro (if you need it) on constructing a base class for exactly this is found in perltoot.

Update: As a template for the autoload code, I give you a modified module

package Foo;
use strict;
use warnings;
our $AUTOLOAD;

sub AUTOLOAD {
    my $self = shift;
    my $class = ref($self) || $self;
    my $name = $AUTOLOAD;
    print "$name in $class\n";
}

package Foo::Bar;
use strict;
use warnings;
use Exporter;
our @ISA = qw(Foo);

sub foo {
    print "foo\n";
}

return 1;
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and script

use Foo;
use strict;
use warnings;

Foo::Bar->foo;
Foo->bar;
Foo::Bar->bar;
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Now if you'll excuse me, I have some documentation to read -- ikegami just blew my mind.