Well, depending on the complexity of your current QlikView documents the conversion to Qlik Sense could be not that straightforward. There are many QV functionalities that at this moment are simply not possible on QS, and for other you have to resort to extensions.
On the server side, it's very different and QlikView Server and QlikSense server are different products, so you would need to get a new Server license. Also, the license scheme is different in QlikSense, where you use Tokens which aren't the same as the usual QV licenses.
Maybe you should ask your local Qlik Partner for a demo of Qlik Sense to get a better idea.