Do i need an extra cable to fit the standard skoda HU? Thanks

No. Enjoy the kit they are fantastic. 

As above.

You may need to hide the blue box down out of the way, as there isn't much space behind the radio for it all.

On mine the blue box is behind the trim to the left of your knee.

Thanks, Think it will fit behind glove box?

Yes thats where mine is. 

Thanks.