Have you tried whatever you've said above? I believe the best way to answer all your questions is to try them. I'm sure each one of us have faced your situation before, but that would be under differrent circumstances. All your questions are practical and it would defenitely be answered once you try to stimulate those problems.

That being said, there are several ways of coding in perl to make the logic work faster. One way that you could time the responses to your code would be to use the benchmark module.
Once you have done your "testing", please let us know also. All the best!