It's been a long time since I incubated panthers so I'll defer to others on acceptable temperatures. Yes, you can keep them too hot. Too hot is very bad, worse than too cool. Too cool just takes longer. Too hot kills them or makes them hatch faster and weak.
Your egg container should be close to 100 percent humidity. I use plastic shoe box type with a slightly loose fitting lid, no air holes. I've seen a few people use tight fitting tupperware type, with no air holes. Not sure how they are getting away with that unless they open it every couple of days. There should be some air exchange, but very slight. If you let in too much air, the humidity goes down. If you don't see condensation inside the top and on the sides of the container, chances are the humidity is too low. The inside should be covered in tiny droplets after a few days. I consider it just right when the eggs take on a translucent appearance.
Good luck.