You are welcome brother. Perhaps you are the first one here on PW who went as per my suggestion. Am fairly pleased for it. Perhaps it would be the best thread ending up properly.
For oil filter change, OMG..... please never go to Toyota again. Leepon's filters are best and price is only Rs. 260~270. So next time, try for leepon but original Malaysian one.
As an experiment, you can buy 1 leepon filter, open its top and take out the filter paper inside to check the quality and compare it with Toyota's. I can literally say, there will be difference as size of mountain.
For Octane booster, a word of wise. Plz don't use it in your new Belta. I've tried it in my pass 1kr-fe (same engine as belta) and can hear bit of the knocking in the engine. So if you have another car, then use it there. But not for belta.
Procedure to use it already mentioned over the bottle. Its 150ml liquid already sufficient for 70L petrol.
So first, fill the tank (go for auto fill. Not for manual fill). After that pour half Octane booster in the Petrol tank.
Save other half for next time.
And for the safer side, never buy this product again (Octane booster or injector cleaner, etc.) Because these additives doesn't produce any significant charm in driving and just easily pull money out from our pockets.
For 20K mileage. Yes he informed the same to me as well and I generate a separate thread to have expert's opinions. But 20K interval for small engines seems too much. Am presently running it at 2K and engine's drive is getting smoother everyday. However, 10K changing interval seems sufficient but don't forget to have the oil filter change after 5K. Use leepon's oil filter or I can assist you to buy 10 oil filters together at the price of Rs. 2550 only for your belta.
All the best.