For both CPU and GPU I would recommend 40C while idle and no more than 85C under load. Heat is the main reason why gaming laptop die and high performing laptops generally produces a lot of heat.
I would recommend a laptop cooler to help lower temps. However, a laptop cooler effectiveness depends on the design of the laptop chassis. Based on my experience with the Lenovo IdeaPad Y470, the chassis is not designed very well at all for laptop coolers. I have a Coolmaster laptop cooler which allows me to strategically move the two fans around the cooler itself depending on where the air vents are on the laptop. Even placing the fans under the Y470's vents, the temperature did not drop.