Hi Kipek and welcome!
Servicing - what area of Sydney are you looking at? My experience with an independent BMW specialist has been great, particularly if you're interested in getting the job done right.
Fuel - Shell V-Power and BP Ultimate 98 preferred, however I've not noted any issues with Mobil 98 or Vortex 98. In my case, choice is typically limited by geographic availability. Seems to run ok on 95 when 98 is unavailable.
Tyres - the big question here is RFT or not. There's a lot of discussion on this forum and others about RFTs - for me, RFTs are the better allround choice. As you start to look into RFTs, you'll discover that your choices are somewhat limited by wheel size and manufacturer. It'll likely be Bridgestone, Pirelli or Conti. Michelin have a very limited range of RFTs, which at last check are 911 sizes, not 130i sized
I can't specifically comment on the 18" options as I'm running 17". Either way, have a look at the threads here about Tirerack, as you'll be gouged locally for RFTs.
Moving away from RFTs will open up your choices significantly, but there's other compromises, but they may not be significant for your situation (eg no other drivers of the car, availability of jack/repair kit/spare).
Daniel.