As a rule, yes. Nowadays it's almost impossible to get everything needed from food. In order to figure out which vitamins you need to take, consult a nutritionist. If you look for a good supplements shop, I recommend this one https://vitasave-us.com/. Despite the fact, that I keep a healthy diet for many years, I take a lot of various vitamins on a daily basis.
No, indeed, taking supplements if you already have a properly balanced diet can actually be damaging.