Calculator layout - grid or flex

Hi, I’m a bit annoyed beacuse, after 4 mounths since I began the fCC curriculum, sometimes it seems that I have not understand flex and grid yet. In particular, today I bagan the jS Calculator, which I want to do with React. I selected Flex box, realizing that maybe was a bad idea, and I took the Grid system, and here is the result, I mean, the result of the layout that I wanted to achieve.

Actually, it works like I want, but I was trying to understand if I can achieve the same layout with Flex Box, even if it works not exactly in the same way.

Actually, my problem is that every month there is a day and I realize that Flex and Grid sometimes are not so clear (but man, I really have read SO MUCH tutorial), or maybe, I don’t plan the layout in a good way.

So my question are:

  1. Is there a way to achieve the same layout of my Calculator with FlexBox?
  2. Any particular suggestion to improve Flex and Grid (NO games, please, I 've already done them)?
  3. Maybe the problem is, that I don’t plan enough? In this case I think I need more structure every time I start with a new Project (stages, objectives, targets ecc). Any resources about this?

Thanks
Nico