I'm currently in the process of creating a game for the WP7 marketplace. I havin't been throught the process of publishing it to the market place yet but was wondering if there are any pre publishing steps I need to know about? Do you need to register an ABN to recive income for an App and are there any tax implications?
How to start a company is really too big of a question to ask here. There are so many aspects to it, it is really quite complicated. If you are set to do so I would highly recommend getting an accountant or similar to assist you with it.
I would also recommend only do so if you really need to. Remember a business is different from a company. If it is just your business name you want now, then register a business name (I think it's under $100). Then you have your name for branding and you can always set up a company behind it later on.
The company itself is complicated and gives you many obligations annually. The items you have mentioned really just scratch the surface.
As for sole trader, you are correct that you need an ABN, but GST is also something you need to deal with if earning over $75,000 or it might just be a good idea for the tax benefits (you can claim 100% of all GST in your expenses). Again I would recommend getting professional advice for this.