З днем ангела!

It has religious origins, but today it is a general cultural tradition used by both religious and secular people.

It's not mandatory like a birthday, but flowers or chocolates are always appreciated.

Most Western names have an Orthodox or Catholic equivalent (e.g., John = Ivan). If not, you might not have a traditional Name Day.

Yes, it is very polite and professional.

In folk tradition, the patron saint is often called an 'angel' because they are seen as a protective spirit.

Usually, only the first word is capitalized unless it's at the start of a sentence, but in greetings, people often capitalize 'День' for emphasis.

Simply say 'Дякую!' (Thank you) or 'Дуже дякую!'

Yes, kids love it because they often get extra sweets!

'Іменини' is the formal noun for the day; 'день ангела' is the most common way to phrase the greeting.

Yes, it's an annual event on the same date (depending on the calendar).