gear question .. mic lead for pro70

wim

hi there, i've just received my AT pro70 mic and it's sounding pretty good on first try .. i just have a few questions. it needs an extra lead out of the filter which doesn't come with the thing. currently i'm using one i had lying around the house , which is just a long mic extension lead with those fat 3 pin connector at each end (i think it's called XLR?) then a little attachment on the end which converts it into a plug looking like a regular guitar lead. the attachment thing has a switch on it for high impedance and low impedance, both pass through some signal into a guitar amp but the volume is lower on the low impedance setting.

1. my mic lead is stupidly long. will i get a significantly better sound quality by using a shorter cable, like e.g. this 1m one? or would it be better to put a preamp near the input instead?
2. if i were to order that item, would it have the correct impedance to play into a guitar amp? or into a computer to record after using a 6.5mm -> 3.5mm miniplug sort of adapter? i don't really understand the whole impedance thing

wim

3. would something like this XLR to usb work better than miniplug jack in the soundcard?