I am looking to buy a cd player head unit to replace the stock cassette player in my fabia 51.

Is there any specific specs that I need for it to work with the fabia?

Ive looked at a few specs around and see 4x 40w. I know that it was to be over 40w else it will be very quiet. I take it that the 4x is the amount of speakers.. does this include the tweaters?

I need to buy a faceplate to fit aftermarket HU's and also a wiring loom.

My budget is around

You don't need a wiring loom as the Fabia already has ISO connectors, you do need the adapter plate though, around

look around places mate, plenty of mp3 cd players for under a ton. a lower number power wise won't make things quieter, it means that it will distort easier, they will both go the same volume just that a more powerfull one will sound better at high volumes

also try www.caraudiosecurity.co.uk

As said above, you shouldn't need any extra wiring, although you will probably need an aerial amplifier if you're bothered about listening to anything on the radio after you change the HU! Something like this should do it, but I can't say for sure aside from saying that I needed one in my 51 Fabia Comfort

You can get a faceplate for the HU from different companies. Check with your dealer first though, as I seem to remember someone saying they were a fiver or something?

On the speakers front, you should be able to get by with the current fabia speakers. I've had a Kenwood CD player, and now a 4x52w Sony MP3/CD HU and they've both sounded fine...

A Fascia plate is about