This is very good advice. I run almost all of my guns stock. I don't have an inclination to accessorize and I only make a change if it positively impacts the experience of handling the firearm, particularly in increasing reliability, ease of use, etc. I don't have anything for aesthetics, and maybe that's just reflective of my rather plain jane personality. In most cases I am quite happy with the firearm out of the box. Some people are very particular about trigger pull weight - for me, the only trigger I have ever wanted to proactively change was on my 10/22. Rest of them, I just run stock and just get used to it.
There are some guns that have specific recommended upgrades. I see you listed the PC Carbine. Well, the only upgrades I have for that are the MCarbo shock buffer and c clip, only because in taking the gun apart many times, I found the stock shock buffer and c clip extremely flimsy. But that was after using it for a while.
There are also subforums in which there are threads dedicated to your specific desired firearm. I believe the PC Carbine has a sub thread (may be a sticky too) in the PCC subforum. There may be value perusing those threads to get a flavour of what others have encountered, both the good and the bad. I know for me, finding out that the WK180's gas block screws come loose was very helpful as it undoubtedly saved me a broken piston rod, which was an inevitability had I not read that thread and subsequently checked and loctited my gas block screws.
There are some firearms that are generally very reliable out of the box. Some, not so much. Some have lots of upgrade options but as with everything else, it depends on each person's preferences, interests, tolerances, etc. No different than cars, really. Some people buy a car and drive it stock through its life cycle. Others like my lady friend, buy a car and start changing the pedals, manual shifter, and a bunch of other stuff which for her, she likes, but for me, I have zero interest.
The PC Carbine, by the way, is a great choice for your first firearm.