Is it okay to drink before 12hr fasting? My test includes blood sugar, lipid profiles and serum creatinine. Coz last test I feel so thirsty.

Water. Drinking a little water should not have a significant impact on result of blood sugar or lipid panel. It may affect serum creatinine, but that should not be very significant either. It is recommended that you be fasting for the tests though.
You can usually. Drink water, diet soda, black coffee -- anything without calories. Check w/whomever ordered the testing.
Yes but! Drinking plain water may not be a problem. Anyway check with ur md.