Yes, PSM is a component of traction control.
http://www.986faq.com will hwlp you with what options comprise the sport package.
As for which options you should get... It's really a personal choice. I would say if Xenon headlights are important than find a car that has them, because they're well over $1000 to retrofit. For me, heated seats would be a must if I had to go shopping again for a Boxster - they really extend the useful season for top-down driving.
If your car doesn't come with PSM forget about it.
ABS and side airbags are standard as far as I know.
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