Being able to use the okay Google voice command (although only while on home screen) is enough for me to use GEL. Also as others have pointed out. I like the Google now integration.
Afaik there is no OTA for the Nexus 4 rolling out. Only for the Nexus 7 wifi so far. But, since Google published the factory images for Nexus 4 and all versions of Nexus 7, you can install 4.4 using the factory images.
No, the OTA update is a stock version of 4.4. Either you go back to 4.3 stock and update from there with the OTA or you flash it directly. You need to wipe you're device for that, though.