I'm going to assume it'll work with the Nexus4, I've used the Sony Smartwatch on a lot of Android phones, wife currently has a Nexus4 she uses it on, currently I'm using it on a PadFone + Galaxy S4. I've tested with a number of other phones though.
I personally suggest just getting the Sony Smartwatch 1 for now, it's pretty much the same as the SSW2 except no NFC and slightly lower resolution. Basic concept is the same. So if you don't like the SSW1, you won't like the SSW2.
I'll be upgrading myself, but even with the SSW1, it's probably one of the best purchases I've ever made. I can't even begin to tell you how convenient it is having a watch there instead of taking my phone out or going to another room to get it