To upgrade or not? Someone will be messed up and cry wolf on the internet. I guarantee it will happen, but these are always exceptions usually caused by problems that were present before the person upgraded in the hopes of fixing their broken system. So don’t worry. Just wait and give the developers some time to make the necessary tweaks so you don’t have to worry about them.
The Apple Watch is, first and foremost, an iPhone accessory. It might be even more than that eventually, a truly independent gadget, but a vast majority of its current functions like making calls, sending messages, getting information, even playing any third-party games.