What are the model numbers of the spark plugs you've bought? What variant is your Belta is it the 1.0L or the 1.3L?
I can't say anything about the transmission oil, if your Belta is the 4WD variant then the transmission oil you have added is fine because the 4WD Belta comes with the common 4-speed automatic transmission used in a majority of Toyota sedan.
If you're Belta has the CVT gearbox then you have made a mistake. You should have added Toyota Geniune CVT fluid TC it comes in a 4L canister.
I haven't replaced the brakes, brake shoes or brake pads yet on my Belta yet. You could probably get a complete brake setup (front & rear) from a half-cut or whole scrapped Belta or Vitz in Shershah or maybe even Bilal Gunj.
Brake pads aren't expensive, OEM ones cost 3,500rs (they consist of 2 pairs, both used for the front ofcourse)
Yes, their could be spacers installed. I hope he doesn't have a CNG kit installed :-#