for lenovo, usually nothing to shout about
but the software can limit your battery charge to 80% to extend the life span, cooling wise you need cooling pad, as the laptop can become very hot.

screen are hard coated with matte finish, the model i bought have 2 usb-c and 2 usb-a.

for camera if you're picky you better try it before purchase, the one i bought camera is worse than smartphone made 10 years ago
the dell lappy i use for work has way better camera in terms of image quality, have front and back too.

thin lappy usually is hotter due to puny heatsink, when the heat has nowhere to go it will transfer to keypad/touchpad, can be doubled as handwarmer in winter !
in Malaysia your palm and finger will be sweaty

for watching movie such as youtube should be fine as it's only using tiny amount of resource, gaming is another heat beast that hard to tame.

Usually won't, but as long as your laptop performance still okay and doesn't degrading then probably no need to upgrade,
The performance changes between generation is very small and don't really worth it unless you have spare cash or your laptop really dying

For levono you can extend warranty in the software and price are indicated in there

if you game, better get higher end of GPU and gaming model, but these add a lot of cost due to gimmicky RGB and hi refresh rate LCD.
also higher cores amount introduce less stuttering than less cores, if your game can fully utilize it.

thick heat sink as i mentioned before, it helps a lot dissipation also prevent the system going to throttle mode, still you always need laptop cooler, or just support is enough to give the lappy enough space on side/bottom for fan intake