Hi Mate,
There is no 'best intake'. People will argue to the death which one is better. Its generally best to choose which one suits you best, or you like te look of, or which price you want to pay.
Several on the market include:
-Carbonio - This is the most basic one - This consists on a replacement panel filter and a new carbon fibre air intake duct thingie. This is best if you want to keep the engine cover as standard.
- Neuspeed P-flo and Evoms motorsport V-flow are ones which are very simalar, basically a big pipe with a cone filter on the end. I currently use the Neuspeed p-flo.
Diblias- is a bit different, but looks interesting.
forge do one which is a proper Cold air intake. It is simalar to the neuspeed and Evoms bt has a longer part for true cold air intake.
All of these except the carbonio involve permanant removable or or modding/reeplacemnt of the engine cover, as the standard panel filter is located inside the engine cover.
Only Forge do a kind of blow off vavle, but I think if you have an induction system as above, it makes a simlar sound to a BOV anyway.
Stiffing up the ride involves either springs and or dampers, or putting coilovers on. I origanally had eiback pro-kit springs on mine for lowering, but wanted better handling and a lower ride so got the Eibach coilvers fitted.
There is no strut brace about for the New Leon. Due to the fact there is no room at the front!
You might want to consider anti roll bars instead and they really stop bodyroll (dpending how thich you get them). I use H&R front and rear thicker type.