Hi, included some articles to get started and a website where you can check stocking.
Articles to Help you Get Started with your Aquarium
The API master kit is the way to go. Congrats on the purchase, the tests last a very long time and are fairly reliable. The tests will tell you if the tank is cycled and stable.
I feed my fish once a day. About as much as they can eat in several minutes. Missing a day say once a fortnight does them no harm.
Q5 - water changes of say 30% to 50% each week is best and cheapest you can do to keep the tank healthy.
I have tropical fish so also have a heater to go with the filter (winter here so tempted to sleep with the fish).