You don't need to mix it all previous, just add the sugar, fill the bottle with luke warm water to the recommended level.
Then add the yeast and baking powder, don't shake the bottle, just leave it to it.
Difficult to estimate the bubble rate, it will vary during the day as the temperature of the room also affects the mixture.
If you don't think you have enough CO2, just buy a T piece and add another bottle, make sure you don't kill your fish though, when I used DIY solution I always had an air pump at light out, it came on just after lights went out and turned off two hours before lights on.