The hardest part was removing the plastic casing surrounding the PS5 itself as it involves sliding the casing off the system. Given that the casing isn't totally symmetrical, it'll take some patience and a decent amount of strength to slide the case off. There are quite a few Youtube videos that detail how to do this without breaking the plastic as this was my biggest fear.
Installing the hard drive itself is very easy. You don't need to have prior experience building PCs to install the hard drive.
If I were you, I would buy a SSD that already comes with a heat sink so you won't have to worry about buying that separately. Look for guides online that list SSD hard drives that come built with heat sinks that are compatible with PS5's specifications.
"Sean sparks like John Starks, nah, Sean ball like John Wall" - Rest In Power Forever Sean Price.