What does this light shaped like a cylinder mean?

If you want to check the capacity remaining in your battery download osiris battery bar from http://osirisdevelopment.com/BatteryBar/. Nice malware-free little app that provides a far better battery meter than windows' built in one, it also has a metric for battery wear which should help you in this situation.

The rubber pads are shims that prevent the components from touching or grating and they provide a little, soft support like a pillow, so that the components are not hanging in the middle of the air but also without having them bolted down. This is especially important for moving components like fans and hard-drives since having them hard-bolted to the chassis would create a lot of vibration and noise; having them sit on rubber shims absorbs the vibrations, creating quieter laptops. They are also insulators that prevent potential short-circuits. Do not apply the thermal paste to the rubber shims!

Yes, those idle temperatures are good and yes, it will be hotter than when you first bought it because the laptop now has a bunch of dust inside it which not only prevents airflow as well as a clean system, but also actively warms the system like a blanket. Unfortunately a fan is insufficient to keep the dust out because dust is mostly dead human skin which usually has oil and other stuff that makes it sticky, so simply blowing it won’t make it go away; it has to be wiped away.

It should come as no surprise that the ambient temperature has a big effect on a computer’s temperature. It may seem like electronics are only concerned with the temperature reading on the thermometer, not the humidex since they don’t sweat, except that humidity does indeed affect them, so yes, 35-42°C is going to make a computer run hotter.