Can I upgrade to a 11 speed freehub or do I need to change everything?
This is a partial answer:

Given that the WH-RS10 isn't a fancy wheel, if you can't just get a 11 speed freehub body, you're going to be best off economically by just replacing the whole rear wheel if you want to go 11 speed. I suspect there isn't a replacement to 11 speed, but you can ask your bike shop or someone else may answer there is. 

Interestingly, Zinn has figured out that you can file the feet of the splines down on an existing Shimano 10 speed freehub to fit a 11 speed cassette on it, since the difference is only a few mm. But this is at your own risk, and may or may not work.