There actually is a regeneration mechanic to the game. Anything that has been touched and not claimed will regenerate over time. It may not necessarily be the same block you found, but it will regenerate.
2a) Every world has different quantities of the various blocks, based on rarity vs danger. So the beginner world with level 1 Spitters will have more iron and copper, whereas the worlds with level 3 spitters and other aggressive mobs will have higher percentages of those ores.
2b) After release (and even a few times during EA), more worlds will be added to each region based on need/population. So, I’m sure we wont have to worry about running out of materials.
Here is a comment I made on another post about the world regeneration, and my way of thinking on why I believe the current regeneration mechanic works: