Thats it, this is known as a panel filter, the Focus already has a snorkol for cold air feed on the standard setup, cones are more trouble than there worth! As to turbocharging there is far more involved to it than that and it would be very expensive to do, the management for example would need changing, different injectors and in some cases fuel pump etc, the exhaust manifold would be completley different as well, these are just a few things!

You might want to look at the 1600 "Ecoboost" engine if wanting to go down this route as this is based on the SE, so you may be able to replicate that setup, if you really are determined and prepared to spend alot of money then go for it but in my opinion it would be better to save your money and buy a faster car, the ST is a cracking car and they are becoming affordable now (A lovely torquey engine and 225HP out of the box and pretty fast as well, plus you get a georgeous sounding 5 cylinder Volvo engine )

You are right a scoop on the bonnet would aid airflow, this is why Subaru Imprezas have one as they have there intercoolers are placed beneath it.

Martin