If you’re opening up the laptop for all these replacements, you should consider replacing your thermal paste as well. If the laptop is over 5 years old, it may benefit from the replacement.
I’d recommend trying to find an ifixit guide or a video of someone else opening up the laptop online and reading/watching that first. Getting to the cpu is usually a little harder than RAM/battery.
If you did all that, it would really feel brand new.