Yeah defo a PID. Yeah you could get smaller element but if you have a 5.5 already just use it. Shouldn't be any issues if you control it properly.

You'll definitely need some measure of control. A pid in manual mode means you set a percentage of output, meaning you have infinite control over the vigour of the boil. Alternatives are a pulse width modulator, or an SSVR and potentiometer.
The pid option will require a pt100 sensor, the other 2 options you can just control by sight.

By the way, you should start a thread on this so that anyone responding gets a notification. I only spotted your comment by chance, could've easily missed it.