[oil pan 4]

The reason why I would chose a belt driven coolant pump over an electric coolant pump is I figure less electrical draw makes for a better alt delete. You can have both, if you know you will never drive the vehicle for more than a few hours before being able to recharge. Once you rule out time and distance between rechargings as a problem then go for it, I bet it will work great.

An actual purpose built electric coolant pump isn't recommended for street use but I have ran mine up 12 hours at a time driving from New Mexico to Virginia. So electric motors and pumps aren't the problem.
I see potential problem with that motor controller. I work with bigger various motor controllers and they all have one thing in common, they like to quit and they seem to do it at the worst possible time.

If your travel situation allows an alt delete and electric water pump to coexist then first try running the motor straight off 12v and if you believe the motor uses too much power then add a big resistor to the circuit and reduce power to the motor that way.
Its not as efficient as a motor controller but its not going to fail.