1: Most don't decide. Most worship all, sometimes even non Hindu ones or modern non scriptural gods like sai baba. Sampradayas you mentioned form minority of Hindus.
2: Hindu worship is primarily an individual act rather than a communal one, as it involves making personal offerings to the deity. Worshippers repeat the names of their favourite gods and goddesses, and repeat mantras. Water, fruit, flowers and incense are offered to god.
3: The purpose of puja is to honor the gods and to pray for good luck in the future. In order to get these good blessings, people offer the gods sweets, flowers, fruit, and other things.
4: “I like the way that believers here find gods that best suit their own beliefs,” Freeman tells us. “It’s like a spiritual fingerprint, unique to each person.”
