Oil filter, cabin filter questions, spark plugs

[dm567]

My 2004 x5 with the 4.4 liter engine just passed the 50K mark and I'm now out of warranty so I have a few questions and like to get the forums opinions: Answer one or all, the more input the better.

1. Which oil cartridge should I buy? Auto barn sells the KandN cartridge filter and the Beck/Arnley Oil filter. Which should I buy? Or should I look elsewhere for a mann filter? The Beck Arnley is 15 dollars and the KandN is 10 dollars.

2. When do I change the cabin air filter and where is it? Have they changed it already prior to the 50k mark?

3. When do I change the spark plugs? Have they already been changed prior to the 50K? What should I buy?

Thanks
D