When it comes to buying replacement parts always go onto the Realoem parts site to find out what your car was fitted when it was built at the factory, using the part numbers then go on to sites such as Autodoc and either search by part number of entering car details to find brands available, always cross check on other suppliers web sites like CarParts4less who are the web based sister company of Europarts but often cheaper than Europarts.
RealOEM.com BMW Parts website. This site can be used to look up BMW part numbers and approximate part prices. The Parts are grouped into diagrams and diagrams are grouped into categories and subcategories
www.realoem.com
CarParts4Less.co.uk are one of the largest online car and van retailers with Cheap Car Parts for every make and model from leading high quality brands.
www.carparts4less.co.uk
Don't forget to use their discount codes that appear on their home page to get current discount offers.
Spark plugs choice is down to your budget as to what type you go for they will all work ok, some brands will have just one base electrode others such as Bosch will have 4. They will all produce the required spark.
Just looked at Real oem site for a year 2000 Z3 2,2i car as there isn't a 2.3 listed like you quoted so think you may have quoted an incorrect vehicle.
Go on Realoem site and put your last 7 letters and numbers in the Vin search to see the exact model of your car and its associated applicable parts.
The 2.2i is fitted with individual ignition coils that sit on top of the spark plugs so do not have ignition leads like the four cylinder 1.9 cars.
As to air filters, stick to the standard fitment, adding cone filters and the like don't do much to increase performance and the oiled type can foul the Maf if over oiled causing more problems than they are worth.