2: You can allow the fish to swim out on their own after you added tank water to the bag. Do allow around 30min-1hour for the fish to adjust before letting them swim out.
3: You are adjusting them to the soon-to-be living conditions.
P.S: senkang zone i know have high level of chlorine/chloramine (ok depend on which part of senkang actually) , you might want to add anti - chlorine/chloramine like seachem prime if you don't trust your water purifier/filter. it don't hurt to be safe.