Crossover Polarity and Inductor?

I am wanting to build a third order crossover network.  What i am confused about is does it matter if the capacitor is polarized or not? The reason why i am asking is that a while ago when i first started getting into car audio, i got some bass blockers but wanted to learn to make my own so some instructions said to get a non-polarized capacitor. So, if it doesnt matter if its non polarized or not, if i get a polarized cap, im guessing the + side connected to the + lead of the amp, then the inductor and the + side of the 2nd cap connects to the "-"

Also, is it possible to create ur own inductors? I am looking to make one that is about 1.2mH.  I saw a formula that on Howstuffworks.com says:

The area and length of the coil are in meters. The term mu is the permeability of the core. Air has a permeability of 1, while steel might have a permeability of 2,000.

I am wondering if that is correct and how i would make one? if i got the right cylinder, would i just wrap the couil of copper wire around that? also if i did, could it be a wire that has a thin jacket over it so it wont short on anything in the car? an

any help is greatly appreciated

ok lets say i need a 50µf capacitor.  would i get two 50µf capacitors and then hook them in parallel with reversed polarity or would i need two 25µf caps hooked in parallel with reversed polarity?  I really dont care about the sound quality. I am just using the crossover for a loudspeaker(the Radioshack 25watt 8-ohm loudspeaker) thats hooked upto an amp that i have a microphone hooked up to so it doenst matter if it sounds really great or not since it will only play someone talking.

thanks for all of the help so far, its helped a lot