i bought Passo 2 months back and gone through all post purchase todo list
let me answer ur queries with limited knowledge i have
1- I put Shell (Blue)
Shell Helix HX7
Havolin is also good but i reckon Mobil 1
2- The sound u hear is coming from drums,get ur brake service but it's normal don't worry.By the way are u experiencing any vibrations with LOW RPM specially when car is cold.
3- No idea about catalyst converter but any thing comes from factory must have a purpose so don't remove.
4- Original CD player looks good but if u want navigation u can easily get it from Peshawar or Lahore market.
5- No idea
6- Using 25% of Hi octane keeps ur engine healthy but not recommend
Suggestions:Get Throttle Body and Map sensor cleaned,Gear oil change and filter service,Plug replace or serivce,Battery cleaned / replace as required.
I am running this car for two month and i found only two issues
1- Steering colum play which can be adjusted easily
2- Vibration at low RPM possible cause (Engine Mount rubber weakend)