You shouldn't leave fish in the bags for more than an hour or so, they will suffocate. How many fish, as few as you are adding should be fine, just add another squirt of bacteria as you fire up the filter, the cloudiness is from the bacteria not suspended matter it's normal and will dissipate. Bettas need a warmer tank 80-90 so a heater is necessary or your fish will be sluggish and prone to diseases. I would also add some aquarium salts, they are good for reducing stress and can also be used to treat things like ick. Follow the direction amounts, they are not necessarily but a cheap addition.