Electric Motors
Some good info on this site. They briefly touch on the subject of overloading. it is Important that you do not overload either the motor or the battery if you wish them to last for any length of time. There are some relatively cheap Wattmeters available that allow you to measure the amps and volts under load and by adjusting the prop you can ensure you are not exceeding the max ratings. GiantShark (ex GiantCod) have these as well as motors and batteries. 😀
In answer to your question about fittings there are many web sites including a few in Aus. I could mention the ones in the UK but I suggest you do a google or e-bay search for model boat bits and choose the nearest supplier.
Dave