Hi Andrew
Welcome to the Forum
First the Dealer is a business and will try to generate Profit where it can. If you are capable of changing Oil and Filters yourself do so and keep all reciepts as part of the cars History
Spark Plugs these are normally mileage based for change or if of course showing signs of failing the same applies to coil packs
Micro Filter and Air filter these items I change annually as the cost is so low
If you are not into DIY then Google the Register of BMW Specialists these garages normally are BMW trained technicians with all the equipment to maintain your car but their hourly rates are often about half that of a Dealership (someone has to pay for the Free coffee) With the BMW Specialists many can register your service records held on the BMW servers and update them.
When servicing my own cars annually I buy Mann Filters Air and oil (OEM suppliers)and Castrol Magnatec 5-30 oil which meets BMW LL04 standards cost is around £70. I carry out the work near to MOT time so I can check the car over. I have my own BMW Diagnostics allowing me to rest any service points and of course find and reset fauts
Dave