Depends on the Ryzen processor you get. If it comes bundled with a Wraith CPU Cooler that will be sufficient for normal use. But if you are planning on Rending or other CPU heavy load type programs I suggest you purchase a 3rd party CPU Cooler of at least 150 TDP rating or higher for a 105 or less TDP processor.
The better air flow you have inside your computer case the cooler your hardware will run and the less energy will be used by the fans running at high speeds due to hot hardware.
As for RAM Memory just go by the Motherboard's QVL List for your processor. Those RAM Modules have been tested by the Manufacturer to be compatible with both the Motherboard and Processor.
You can also check the RAM Manufacturer website and use their RAM Calculator or Finder to see which RAM is compatible with your motherboard and processor.
As to which RAM Manufacturer is best, they all have good high quality RAM so mainly it depends on your budget and how much you want to spend.
In my case, G-Skill Trident-Z NEO are totally compatible with Ryzen processors but again I purchased a Corsair Kit of 4x4 GB Ram when I had my AM3+ Motherboard. That Ram lasted many years (PC on mainly 24/7) without issue before one of the four sticks went bad.
I would just google the RAM you are planning to purchase and read any reviews about it to see if they are good or not. I usually go by the Retailer's Customer reviews one star Reviews to see if I see any pattern of defection with the RAM or with the Manufacturer.
As too:
'Which processor calculate faster - with more kernels or with higher tact frequency?"
Someone else is going to have to answer that for you.
NOTE: I just gave my opinion of the hardware I purchased. Other Users, I am sure, will give you a similar opinion concerning other motherboard manufacturers and hardware.
