1. I'm assuming this is mainly academic because there are accessible non-painted surfaces on most frames even without paint chips. The inside of the seat tube is an easy one to get to, but the insides of any threaded surfaces such as the BB or derailer hanger are others.
2. I'm leaning aluminum on the pictured bike above for the reasons already stated.
3. You could probably figure it out by how fast an ice cube makes a given section farther away cold, but you would need an aluminum or ti bike to compare to.
4. If you can't tell by sight and ride, does it matter?