Weather will be a lot warmer than UK.You would be very unlucky to have any prolonged rain.Most bars will be open.24 hr sq will be same as UK, busy on weekend.
There are at least 8 bars on, or just off Ave Teleponica hill,outside H/Bali.The Pickwick run by friends Brian and Ann,and the Albatros run by friends Alan and Jim. Two good bars to start the night.
There is a Indian resturant on the hill if you feel peckish after a night out.Also I can recommend if you walk up the hill,the Chinese on Ave Bonanza where you will find more bars.
Up that direction you have the Elefanti bar where they have live acts.