Overlap between computer science and chemistry?
Have a look at list of computational chemistry software. It gives you overview, how the computers are used in chemistry. Many of them fall more into the chemical physics field, some into the chemoinformatics, to name just few. So definitely there are lot of places to contribute to use of computers in chemistry. If you are able to mix the software engineering and the science itself in a good way, possibilities are immense.

As for the last question - almost whatever field of chemistry you choose, you can contribute to the programs used within it. There is no such thing like completed scientific code. And university level is a necessary prerequisite to do reasonable science. Just concentrate on the models and mathematics behind the scenes and everything will follow.