G'day Hannah. As you can see we're quite the welcoming bunch.
From another Aussie, welcome and enjoy the forum.
I can say that the 12-24 will give you the best landscape shots you could ever take. A very fine lens that I use often. The 55-300 is great in good light, and it can even double up as an OK portrait lens. Lean to use the Av mode to start off with, which teaches you to control your "depth of field" and create the type of effect you want in a landscape (usually with smaller apertures, which are bigger "f" numbers like 8-16) or a portrait (usually with larger apertures like "f" numbers 4-5.6).
Enjoy shooting. That's the main thing.