Yes you can. Most electrical appliances will work if supplied with power that's within 10% of their voltage rating.
Yes.
no
Yes
Yes.
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.
Take the plug in your hand, and insert the plug into the wall outlet.
No. First off, the plug will be different. And even if you replace the plug, it won't work right on the wrong voltage
You sure can. It will run a little faster.