Flex Pipe/Cat/Filter question Options

[elvasoshexai]

uh... when i get exhaust done for my turbo project... i was gonna get a cat + flex pipe put in.. so... i was wondering if these are ok:

cat:
http://www.car-sound.com/02product/universal/mirror.asp
or do i need one that allows an o2 sensor?

for flex pipe, does it really matter if i get a cheap one or not?
and what length do i need?
i was looking @ vibrant... they have a standard flex pipe w/ inner braid liner or an FI series one w/ interlock liner
the lengths range from 4" to 10"
here they are:
http://vibrantperformance.com/catalog/inde...db3b514c2016f1d

now, for an intake filter... what size do i need since they come in all sorts of shapes and sizes?
i was looking @ the round/straight and round tapered:
http://www.knfilters.com/universal/universal.htm