Welcome to Redback Garrison, Kevin.
You should find plenty of help here, especially being in Brisbane. There are many things to consider when picking your first costume, 1 of them is the weather. The Shadow Trooper is indeed an awesome choice and I am one to push for more Spec Ops troops. However you may also want something that doesn't attract too much heat. I myself am a Shadow Scout, but my first armour was TK (Stormtrooper) and I will soon be getting a white Biker Scout for those warmer days where I want the mobility of a scout.
With weather being one, another consideration is the brand of armour. We have a local seller here in Queensland, I believe you'll need to contact Apok. And there are other sellers world wide. It can depend on your body shape too, being a person of larger than average I found that AM armour was good for me, but I still prefer to buy my helmets from Apok.
But yeah, I'm sure Muppet is already helping you and as he stated check out the Spec Ops site. Also keep an eye on the upcoming events for Armour Parties.