Just beat Chapter 2 of the World arc

I can't play Nyan Cat until I answer this lol. A very important decision...

Chapter 3, go

The standard way to clear stages is to beat Chapter 3 of the World arc, then Chapter 3 of the Future arc, and then Chapter 3 of the Space arc. I personally waited until I collected all the best treasures before moving on to the next chapter.

When you get stuck while clearing Chapter 3, it's a reasonably efficient progression method to farm treasures and push Gurre to get more key characters.

Just as you want.

Are all the treasures up to chapter 2 considered top-tier?

Or make it first before clearing the 3 rooms, go.

And chapter 3 first.

Chapter 3

Clear through Chapter 3 while collecting treasures in each chapter of the World arc, then do the same for the Future arc, then the Space arc. Clear the 'Gure' stages intermittently until the end, then clear Chapter 1 of the Legend arc before heading to the Demon Realm arc.