It'll work just fine for stock speeds, like it was intended to, but the 212 Evo would be better, of course.
If you have plans on overclocking, then definitely get at least a 212 Evo, but if you won't ever overclock, you don't really need to. The temps will be lower with the 212 Evo, but you won't be reaching dangerous levels at stock with the stock cooler, either.
Overclocking and paying for an EVO is definitely worth it. It's like getting a whole new CPU for the price of the cooler. You don't need to do it now, but it'll be worth it in a year or two, so you might as well get the thing installed right off the bat. It's a drag to change.
When I buy a cpu I don't ever use the stock heatsink/fan because it is just a basic cooler that is just good enough for ordinary Pc usage. Today almost everyone plays some type of game and most people want to do some type of overclock.
Most likely if you bought th K model you want to do just that and to protect the cpu from excessive heat you will need an afternarket cooler. If you plan on a mild overclock then the Hyper 212 Evo will be a good choice. If you have plans on going over 4 ghz then you will need something better and I would read this article.
and what is more ideal 8gb or 16gb could you tell me advantages and disadvantages
It will depend on what you ae using the computer for and why you feel you would need more than 8 gb. For gaming you need only 8gb or less , for video rendering and graphic 3D modeling you would need more.
The pointy stuff you are referring to is the heat spreader and it is how the ram stick dissapates the heat. The heat spreader does not generate any heat , the ram chips do that and the heat spreader is a sort of cooling device. You can get the ram sticks without the tall heat spreaders if you want.