Check valve in radiator cap malfunction, replace radiator cap.
Check to see if the coolant fan is running. With the engine hot, and running, open the hood and see if the fan is turning. If it's not, then either the fan,temp sensor, relay or wiring is bad.
Levels are probably not fine. Check the radiator not the overfow tank for proper level. The radiator should be full to the top.
The radiator costs about $150 and if you have a shop do it you should expect to pay about 2 hours labor plus coolant. A good estimate would be around $300 to $400 if you have a shop do it. If you do it yourself, around $200.
The lights on your Buick could be out for a number of reasons. It could be blown fuses, faulty wiring, or dead bulbs. Your mechanic would be able to test this.
Usually it is the O2 sensor
my buick century would die but only if i slowed down or stopped after about 3-4 miles....if was a spark sensor? that eventually was replaced?
head gasket may need to be replaced
old fuel filter
Could be anything. Some Autozone stores will run diagnostics for free. Try them if you have one near where you live.
There are 2 fans that would be running while you are driving and that is normal... the compressor fan if you have the air conditioner running and the radiator fan runs to help keep the radiator cool while the engine is on.