Question about current
The current in the circuit loop is indeed constant. It must be because no electrons are lost and current is just the movement of electrons.

Indeed ground is not a good conductor, actually it is a bad conductor. This results in more voltage drop for the same current compared to a more conductive (less resistance) wire. This is described by Ohm's Law.

The current indeed depends on the circuit. The current is determined by the voltage V and the total resistance R. Then Ohm's Law states: $$I = V / R$$ where I is the current. So a smaller R (less resistance) results in more current.