Welcome to TRT! most would recommend at least a 30 gallon for a beginner... the 40B (40 breeder) tank is a very common size that a lot of people like for reef tanks.
I'm not much help with fish, I'm running a 10 gal nano as my first reef tank... I have 1 occellaris clown and 1 yellow watchman goby... I'd probably do a pair of OCC's and the watchman, and look in to some other fish to go with them in a 30-40 gallon...
easy corals that I started with are green star polyp, kenya tree, and mushrooms. They don't have a lot of requirements, and were OK with my lower power lights although I didn't have a lot of growth with the cheaper lights...
don't get ahead of yourself though, your first investments need to be to get the tank you want, get it set up with salt water, rock and sand (if you want sand...), a powerhead or two (aim for 30-50x tank capacity for your flow rate), a drop test kit (like API saltwater and reef master test kits), toss a frozen shrimp in the tank and then sit on your hands for the next month. It will take about a month for the tank to cycle in order to be ready to sustain life in it... if you add fish/corals/inverts before that you'll just be wasting your money because they will die in an uncycled tank.
If I were to start over I would go with a 40gal breeder but I started with a 55gal. I would look at cubes as they are apt to have more depth front to back, and make rock scapeing much easier. The 55's limit your fish to a left or right world, cubes are 360 degrees.
Its all up to you and what you have spend. The 40 is a good one. Like ynot said not a big fan of them it was my first tank aslo. After that all of the standard sizes are good. I have a 75. Even though its not much biggger than a 55 its way better. Even the 50 isnt a bad tank
I would recommend passing on the 55. You want something that will be wide enough to aquascape the way you want but that will allow you to clean all around the rocks. Any of the "breeder" tanks (40,50, etc), cubes or a 75 are good tank sizes.
For fish, to start, clownfish, gobies, chromis...things like that. Just not damsels.
the amazon tanks appear to be REALLY over priced... I don't know prices in australia, but locally I bought my 55 gallon tank, stand, and hood/light for $100 used... and even that I wouldn't do again since petco does their $1 a gallon sale every couple of months I could buy a $55 tank and build my own stand that would be a lot nicer than the one I have...
as mentioned above...the 55 will be narrower front to back which makes for bigger limitations on layout of live rock. I would go with an 18in minimum because of the aquascape which is vitally important in a reef system. You will appreciate the extra width over the 55 when trying to place corals....
a general rule in saltwater is "the bigger, the better"! within reason, this is true. as Mahmoud suggested, the larger water volume will be more forgiving of mistakes. parameter swings will be less.
practically speaking, id suggest either a 40b or a 75g they are two popular choices for beginners and more advanced guys as well. its bears repeating that a standard 55g tank is considered one of the worst tank sizes for saltwater. the narrow front to back profile limits aquascape options and doesn't allow for easy cleaning.
personally, I have a 4ob and am very happy with it. it is big enough to keep pretty stabl without a crazy maintenance routine, yet small enough to be manageable. the 36"x18" footprint allows a lot of aquascape options as well.
fish and coral is a tough question. you need to decide if you like fish or coral more, lol. some fish are not "reef safe" and will eat coral. so if you want coral, you have to be aware of that when purchasing fish. as for corals, take a look around places like www.liveaquaria.com, www.cherrycorals.com, and other sites like that. pick out some that you like and pay attention to if they are soft corals like mushrooms, leathers, and polyps, LPS corals like frogspawn, torch, hammer, and brain corals, or SPS corals like montipora, staghorn, and acropora. deciding what kinda coral you like now will enable you to set up the tank and choose equipment to best suit that animal.
thanks so much everyone and listening to guitarherowanab i think i will go for a 40 gallon tank with coral only and another interconnected tank which will be a small reef with compatible fish and coral
just remember, if the tanks are connected and share water, they will both need to be the same "environment".
for example, an sps reef is a low nutrient environment and a soft coral lagoon style tank is a high nutrient environment. you really wouldn't want to have one tank sps and the connected tank soft corals. itd be a compromise, one way or the other.