Apple - USB Power Adapter - White

The wattage of the adapter will only affect the speed at such your device charges. So yes a 5w adapter will charge an iPad but at a significantly slower rate.

The ones I've ordered have been yes.

Yes it is both 5 Watts and 5 Volts (1.0 amp). It is also a smart charger that will automatically convert 110 volt or 220 volt input to those figures. Here is a good discussion on these chargers. https://discussions.apple.com/docs/DOC-3511

Apple recommends the 5w charger for Apple Watch. Higher watt chargers recharge more quickly but over time they can degrade the battery and shorten its lifespan.

Yes you can use a 10w or even a 12w power adapter for any “I” products. The higher wattage will charge faster but the “I” product will only take as much charge as it needs and will not overload.