1. They probably get their fasting rewards if they do bad things at night, but they still got sins from doing that bad things at night. Its just that if you do it during the day it invalidates your fasting rewards and all you get is hunger and thirst.

2. Dinner party is a cultural thing, because we didn’t eat during the day and we have the same time to break fast, it became a party because everyone do it at the same time and usually at the same place. But the day of breaking fast (the Eid Iftar), you are supposed to eat in the morning to declare that Ramadan has ended and you can continue eat at day.

3. Another cultural things. Here, it happens few days before the end of Ramadan. The government mandates company to pay bonus during religious celebrations (christmas for christians, eid iftar for moslem, chinese new year for chinese, etc).

1- You should abstain from bad things all year round everyday. In Ramadan, during the day, you shouldn't eat, drink, smoke or have sex. This will nullify your fast if you do instantly. However, other things such as lying, backbiting..etc it's also bad and you should abstain from it as much as you can.

2- Big dinners are everyday at sunset. Some people/cultures have several meals before dawn, some other prefer to have just one or two.

3- Nobody get gifts. Usually, it's kids who get new clothes during Eid and they also get money gifted to them (usually small change and can range between $1 and $20 depending where you are). During Eid its required to visit family and friend in their home.

"Supposed to" is not the language I'd use. People feel motivated given their self control for food and water and are encouraged to try and use that momentum to also be better people.

In my personal experience as a compulsive snacker being able to fast daily for a month makes me feel like I can do anything