Spark plugs-- use original equipment or at least the same design. Stay away from Splitfire or other such "miracle" plugs. Equally important is to apply a light coating of Neversieze compound on the plug threads before installation. This'll help in removing the plugs next time. Every so often, somebody reports on not being able to remove a spark plug from their engine. Neversieze prevents this problem.
K&N filter-- I'm not a big fan of this product. You're trading air cleanliness to reduce restriction of air coming in. This is only my opinion. For more discussion on this matter go to the following web site and click on air filters: