Is PinePhone good for me?

[ryo]

I write to you from Spain, and I have a few questions about PinePhone. I am a fervent user of linux system, using it daily on my computer. But I'm not an advanced user, and don't have high knowledge about it.

So the question is: I would love to buy PinePhone for me, is it possible with my linux level?

yup.

The other question is: are they going  to sell another Manjaro's version again?

No idea.

The other question is: If not, is the KDE version easy to use?

Depends on your definition of "easy".

The other question is: which is the easier OS to use? 

Again, depends on your definition of "easy".
Because finding something easy is never based on a scientific fact, always based on first hand experience.

Also depends on what you want to use the Pinephone for.
Daily driver? Either Mobian or Arch, although it seems like Manjaro is catching up too.
Even then, you'll need to be able to self configure and tweak many things before you can use it exclusively.
Perhaps you never will use it exclusively, or maybe you will very quickly, it depends on how you define what a smartphone is, because a Linux phone is not a smartphone, it's a small PC in your pocket with phone functionality.
Think PC as a phone, not phone as a PC.

And the ultimate: could I use Whatsapp on it?

nope.