I'd definitely recomend the switch to bmc its nowhere near as loud as the k&n which sounds a bit like a loud fart, no offence i thought it sounded awesome while i had it, changed my mind when i wen bmc.
dont be put off by the lack of noise it grows on you and sounds so much better i burried my cold air feed in front of the battery and the sound reverbed in the wing and sounded awesome, like there was alot more than a 1.4 8v under the bonnet.
i put my own kit together mate for under £100
i used to have the same car as you and had the k+n to soon you will notice it will start to fill with oil! you need to hack apart the old airbox and cut the one way valve out of it so it lets air in but no air/oil out. theres a pic of it below as i took mine out, otherwise your engine will spit all the oil out and no oil isn good
i think it goes on the breather that goes into the right side of the k+n
you are right in saying you will need another breather for the cda but they can be picked up of ebay for cheap.
You need:
CDA 70 - 130 i think
Silicon Reducing Elbow 70-50 (90 degree)
Suitbale jubilees
The way i did mine i order a silicon coupler think i got a 68mm one as it does fit on the bmc and attached my k+n cold air feed to the bmc with jubilee clips as the k+n hose was pretty good and looks good to.
i also made a bracket out of a few fixings i got from focus diy.
here are some pics of mine below:
after and engine bay tidy up
id really recommend a bmc there awesome, but id sort that brerather out first before your engine start spitting oil which i bet it already has!
got any qs just pm me