1. The literal meaning of 欢迎光临 is somewhat along the lines of “Thank you for welcoming us with your presence”. It is used almost exclusively in retail establishments welcoming customers.

2. The word 老板 is used a lot more often in Chinese than in English, as it’s a term of respect. 请问您是这家餐厅的老板吗？

3. 曾经 refers to the experience of doing something before.
a. 请问你曾经在餐厅工作过吗？
b. 我几年前曾经在一家咖啡店打过工.

4. 刚好 is used when you reach your goal quicker than you might have hoped for. 他刚好是餐厅的老板.