Oh how fast people forget.. Did you forget that people said the iPad wasn't standalone because when it was released because it needed a PC or Mac to set it up and sync?! Back then many argued that it wasn't a standalone device.
I see you are confused. The 42mm and 38mm chargers are the same size/diameter. So you can charge different sizes with the same charger. Their accessory page shows only one charger with different cable length not different watch or charger "size".
1) If it says IPX7 rating then it is that. It is not a device you want to go scuba diving with. 2) You clearly trolling regarding the battery life. Yes.. a device battery is affected by how you use it.. shocker!!
I looked but couldn't find anything saying you can't. So it looks like any band can fit any watch as long as you choose the correct size. This is nice since I really like the black Sport band for every day and I want a leather one for certain occasions.