1, your understanding is totally correct, 前面 here means in front of somewhere, this saying is like " let's go to eat at the near restaurant" in English. 2,“这儿怎么了” is " what happened here", but sometimes in different contexts we have different understanding. in later days you will know how to use it in daily life. 3,十几年了，here means over tens years while less than 20 years, and only this meaning. what we say a vague number we say" 几年了“ several years, or when we wanna express about around 10 we say " 十年左右'