<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Can these "buddy passes" be used to pick-and-choose flights or do they have to be used with connections determined by Southwest? </div></BLOCKQUOTE>

You should be able to pick and choose. Making the connection to your international flight will be YOUR responsibility.

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Also, do I need to "list" with the system beforehand or can I/should I do it at the airport? </div></BLOCKQUOTE>

Beforehand, definitely.

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">And finally, should choose the earliest flight out so I can keep my options open, or would it be safe to get on one that arrives a little closer to the international one's departing time? </div></BLOCKQUOTE>

DO NOT risk going close to the international one's departing time. Any number of things could happen. South West could have a delay or cancellation or they could end up protecting a bunch of passengers from another carrier that would bump you from the flight. Go early, early, early if not the day before to ensure you get to LAX for your international leg.