I'd look at the BMC Race RS if I were you... The K&N won't give you a huge difference in performance.
As for will you need to rejet/remap, ask yourself what would be the point if you didn't

The main point of a performance filter is to pass more air, which in turn means you need to pass more fuel, so if you didn't need more fuel then logically, you're not passing noticably more air. You can maybe get away without it, but IMO at best you're wasting your money if you do that, and at worst you could run damagingly lean if you're unlucky.