One of the best cleaners you can use is salt. This acts as an abrasive, much like Comet Cleanser does and it will not hurt your fish. The only time, however, that you would need to use a cleaner would be when you first set up a tank, especially if it is used and the prior person did not clean it out or if you were sterilizing your tank. I prefer having more than one. Catching fish is so much easier if you use one net to chase fish into the other to actually catch it.
Nets come in several sizes.
You will need it to take the new fish you bring home out of the bag. After your fish get larger then get a net according to the size of fish you have. It is much easier however to catch a fish in your tank with a larger net. Though taking a fish out of the bag is much easier with a smaller net. These are an essential part if you have an aquarium.