this is a very open question. With 31 QVD files and 2 billion rows, too many things can go wrong. In order to handle this volume of data, a developer needs to be experienced in Qlik data modelling, and know very well how to handle large data volumes in Qlik. The worst mistake a company can do is to require a novice to handle 2 billion rows.
I strongly recommend that your company contracts an experienced Qlik developer that know how to deal with large data volumes.