Small holes are ok. They won't keep the balloon from flying. If desired, attach the tether line and name and address tag. To launch the balloon , hold the bottom, open end of the balloon over the hot stove and allow it to fill with hot air. The cold air is more dense and sinks while the warmer, less dense air in the balloon rises.
Convection is the action of warm air rising and cold air sinking.
The balloon will stay afloat as long as the air in the balloon stays warmer than the air around it.