Yeah you're definitely right. Don't miss 120fps. But hdr 4k yup.

If your screen is only 60fps thats as high as it can go. You'll need a screen that supports 120fps. But you'll want a screen that supports 4k if your upgrading to a ps5.

Also have a look here, think there missing a few games though. https://www.psu.com/news/all-ps5-games-that-support-120-fps-the-smoothest-games-on-playstation-5/

Try Amazon, its pretty cheap. And you can find tutorials on how to do it online, but im not sure how easy it is to do but you can check and see if your comfortable doing it.

It could be the thermal paste! You can replace it yourself, although i have never done it myself my friend has and he said it was a lot quieter after it.