Is there a minimum distance required between my water tank & water pump?

What about between the water pump & accumulator tank?

Water heater & water pump?

Water heater and surrounding walls?

Anything I've forgotten?

I suspect your question is in regards clearance so it does not ignite items that may be close by. I don't know what brand of water heater you have.  And each may differ.

But my water heater has a foam insulation around it. I would suspect I could place pretty much anything next to that, Because the foam surrounding the unit would catch fire before anything sitting next to the water heater.

If you are concerned about pressure.  I would find it hard to believe that the items you listed would care if the were 2" or 2 feet apart.