Anti-freeze is only necessary if your cooler is set to go down to temperatures approaching zero (if you disable the pump/stirrer) (or zero if you keep the pump/stirrer in service). The Maxi 110 is usually factory set at 10C or thereabouts. So anti-freeze isn't necessary. (This can be changed by adjusting the internal thermostat)
Don't use Ethylene Glycol, as not only is it poisonous but it provides a particularly slow and painful means of death, especially if taken frequently and long term (as through a leaking pipe)
You could add say 10% vodka to the water, this would lower the freezing temperature and a leaking pipe might be quite pleasant but you may need to top it up as the alcohol evaporates.
If you take the pump to bits, give it a good clean in washing soda and then lubricate the bearings with grease it can be quietened down considerably.
That's my experience anyway.