Help with new garage floor

I want to remove my crumbling, powdery, cracked, un-level and un-even concrete garage floor and replace with quarry tiles.

Is it just a case of digging out all the old concrete back to earth and pouring some more, making sure it's flat and level this time and of a decent quality mix, then tiling over that?

Or is there another or beter way?

Any hints or tips?

How deep must the concrete be?
Is there anything else I could use as a substrate?

Thought about epoxy flooring but it seems too expensive and I love the idea of quarry tiles.

If you only excavate to rubble/hardcore you only need 100mm of concrete, but if your down to earth need also need 150mm of hardcore.