By the time I post this, I'm sure I'll be the third person to say the same thing, but the first place I would look for answers like this, is here; using
Super Search. Or, always Googling for something like
Perl Hashes. Either way will usually get some good information for you.
Next to that, I'll do my best in answering your questions:
1. The only limit for hashes are amount of memory you want to use. I've been able to drain over 2GB of memory at times due to data structures, like a hash, that are just too big.
2.
use/
require may only be half the battle. Take a look into creating global variables in Perl. I've found some of the following resources to be usefull:
Hope this helps, and good luck!!
Update
perlmonks Hash Q/A might also be a good place to start your adventure!!
---hA||ta----
print map{$_.' '}grep{/\w+/}@{[reverse(qw{Perl Code})]} or die while ( 'trying' );