Fellow G15 Owner here,
Here's the ram i've been eyeing to upgrade too, it's 1xr8 which was a bit of a bitch to find out (you'll need to check the manufacturers spec sheet for the specific module at least for Kingston DIMMs, Gskill is still a mystery too me.
As for the screen i've not found any good options for a replacement, laptopscreen.com is seemingly out all the time, i have found screens for an old inspiron on amazon before so maybe they would have something. Otherwise you could call dell for the part alone if they sell it, just expect too be gouged a little if they do.
(which screen do you have btw? is it the 165hz one or the 120hz?)
For software while its a flaming pile download alienware command center if you haven't already, it will allow custom fan curves for cooling (fn+F9) and i just run them at 100% its like 53d but thermals idle between 25-35 for me on both CPU and GPU so i think the trade is worth extending the life of the unit.
Hopefully this helps some!
https://www.memoryexpress.com/Products/MX00116745