Baby could be latching for comfort even when he's already full. If you want to be sure, can visit a lactation consultant, they can check if the latch is efficient
Cluster feeding is normal. Sometimes baby latch for comfort also and normally newborn will wake up for milk every 1-3 hrs.
Yup it is normal. To know whether ur baby is having enough, check no. Of poo and pee daily as an indication.