Wake the baby by scratching behind the ear or flicking on the sole. Babies tend to sleep while feeding because they get tired quickly. 

No problem but see correct attachment and holding support his head and proper latch followed by burping.

Hi. This is normal. Nothing to worry

Sucking is reflex. If baby is sleeping with nipple in mouth, then slightest movement will initiate sucking.  After teeth eruption,  this may cause problem. If breast size is large, it may cause nasal blockage of baby, if mother is deeply asleep. Better if mother removes nipple from baby's mourh after feeding. Do the Burping,  and then allow baby to sleep.