Exactly ats why not worth 12th gen at this stage when its release so much will need work done so probs be about a year or 2 to even get it stable
Everything changes depending on what the use of the PC is.
How many cores do you need. I can't answer that but you can look at your CPU usage and see if you need more cores or not.
(TIP) if you see your CPU usage % low then that is because your programs need more single/dual core speed so more cores are not helping. ( could be held back by another part but if your in like the 50% usage of the one you have then more than likely the single core speed is holding it back)
Check how much memory you are using if your running W10 8GB is probably not enough using work programs when you run out of memory your PC goes to craw mode.
EDIT for a gaming PC if your playing the newer AAA games then 16GB is really needed the number of cores need on the processor will very from game to game depending on the game engine used for the game (example warzone can use a lot more cores than most games)
A 10700K/ 11700K or if your a AMD fan 5600X/ 5800X is about all the average person needs, for memory get at least 16GB and a decent SSD for storage. (all depending on your expectations and budget)
I use some work programs and have 32GB of memory the most I have seen used is about 24GB