Yes.
Yes. As far as in the US 220v and 240v is pretty much the same thing. People call it 220 but realistically you prob have 230-240v. Get a cheap voltage tester and check it out
Yes.
no
Yes
Assuming the wiring to the outlet has 2 loads and one neutral, isolate one load from the outlet and use the neutral as the common. be sure to ground from the receptacle to your conduit or ground lead. You should also replace the corresponding breaker with a 120 volt single breaker.
Yes, just make sure it is a 220 volt switch.
If I understand your question, Can you run a 110 appliance off of a 220 volt outlet? You could by only using one leg of the 220. You may also consider changing the outlet. Put in a regular 110 outlet and capping off one leg of the 220 in the wall box. You still have a neutral and a ground to work with. I read this as the questioner doesn't want to modify the outlet. Check the voltage ratings on the device. Many electronic devices nowadays can havdle 120V or 240V as it is cheaper to manufacture one powersupply and sell it everywhere. If your device is rated for 240V, you can put a 240V plug on it. If it only says 120V, no dice. 240V will burn it up.
If it does not come with a plug on it, no. If it is made for direct wire, then 99.9% chance is that it is a 240 volt unit. If you plug it into a 120 volt outlet your water will barely get warm.
The bulb will be about half as bright.
Yes
yes
No, it will cause the bulb to blow. A 12 volt light is DC voltage and your home outlet is AC voltage.