Level up regions

Hi, i just want to hear your opinion about what a new player should do.

I started playing recently and i have levelled up some regions: 1) shadow isle 2) piltover 3) demacia 4) frejlord.
I didn't complete them, they are in the range of 9-13 over 20 levels.

What is it better to do? Level up all regions one by one completely (so 0 to 20 then switch) or is it correct to do what i am doing?
What is the minimum level to reach in a region before switching to another?

Thank you in advance

go region by region on multiples of 4 that way you get the most wild cards to craft most decks.

Race to 8 to get the first set of champions (which you already did).

From there: whatever feels best to you.  The optimal ratio of cards:XP would be to either do like DoubleSummon suggests or alternate to a new region every level, but honestly I think its more important to get the cards you want rather than just maximizing your total collection.  For context: I'm maxed in 4 regions right now, and my Ionia is at ~13 because I have zero interest in playing Ionia.

I think you get champions at level 16, I would race to get each of them to 16. Then rush each to the free champion wild card. Then finish the regions off. Either way you'll get there in the end, but getting champions helps build those decks. Just keep at it and make sure your weekly vault gets to min. of level 10 every week for the free champion wildcard.

Most important, have fun, the grind doesn't seem like a grind if you enjoy yourself.