Celebrations and Customs

Q: Is it acceptable for Muslims to say “Happy Birthday” to others?

Q: I live in India. In my locality most of the people are non-Muslim and I want to know if it is okay to take them as close friends and participate in their religious gatherings or festivities and alike? 

Very few greet by saying Namaste how to reply to it? 

Q: Is it appropriate for students (both male and female) to ask teachers (both male and female) to sign or write their names on the clothes the students are wearing during annual or farewell day celebrations in school? And is it permissible for a teacher to do it?

Q: Is it permissible to celebrate Thanksgiving?

Q: Is it permissible for a Muslim business owner to give his staff Christmas/new year bonuses?

Q: Can a Muslim go out to view the new year's fireworks? Even if it be standing by his room window and watching the fireworks?

Q: 

1. Is it permissible for a Muslim business owner to promote his business using adverts with Christmas decorations? 

2. Can a Muslim businessman sell Christmas lights, trees, decorations, etc.? 

3. What is the ruling regarding a person decorating his business with Christmas lights, Santa Clause etc.?

Q: I know birthdays are not halal but if a close person invites me, I need to go. So if I went to a birthday party where there is no music, only relatives and close friends, I will not eat the cake but it seems bad if I don't eat the food they ordered, so if I eat the food will it halal for me? Only to eat the food.

Q: Is it permissible in Islam to wish someone well on their anniversary?

Also, what about cutting the cake in the presence of close family members? Is this permissible?

Q: Please advise on the new "galentines" trend, it is valentines but for friends. It has become a trend amongst the Muslim youth.