Capacitors for passive xovers.

Well, I got my inductor problem out of the way (used thinner wire), but I've still got some questions on which capacitors to use. I've read that with 2nd order xovers non-polar capacitors are prefered, but what about 1st order (3-way 1st oder is what I'll be using)? Can polar ones be used? What about voltages that the capacitors are rated at? Is the higher the better? Does it have to do with the wattage being pumped through the speakers? If the speakers can handle 500w+ RMS (not that my amp can power that) what voltages for the caps should I use? Also, are polyester caps good for being used in an xover? Sorry for all the questions...
Polar capactors translates as electrolytic or tantalum, neither of which are desirable in the signal path, no matter what. Now, given that sometimes large capacitances are needed, such critters are necessary (power supplies are one good example). But it doesn't have any thing to do with the order of the crossover.
The voltage has to do with the power being put through the speaker. 100V is a good minimum value. There's no need to go over 250V, unless you're into something really unusual.
Polyester is certainly better than the run of the mill electrolytic, but of the 'poly' caps, it's the least desirable. I use Sprague Orange Drop caps (polyester) on the test bench, but when I get ready to stick a project into my system, they come out and I buy something decent to put in. Polypropylene is a good choice for most audio purposes. Polystyrene is arguably better, but isn't commonly available in large values. It also gets expensive fast. Teflon? Oi! Don't ask.