Welcome to Salehoo :)
To answer your questions
(1) You only need a tax number if you live in the United States and buy from US wholesalers. I see you are in Australia, so you won't need a tax number to purchase from wholesalers.
(2) Lately we have been emphasizing the fact that profits aren't always huge on eBay, just because there are a lot of people who join Salehoo with the impression they will literally be making hundreds from each item. But we certainly don't mean to imply it is impossible!
I agree, profits of 50 cents would never be worth the time and effort. In actuality, a more realistic figure would be between $5 and $50 profit per item, depending on what you choose to sell.
For instance, check out this post Link hidden: Login to view
Jimmy works part time on eBay, but still manages to make a nice profit from it. There are lots of other Salehoo members with similar examples.
If you can spare just 2-3 hours a day to work on buying and selling wholesale, then you should definitely find you make enough money for it to be worthwhile. Once you are up and running, there are also ways you can cut down the time you spend on it. For example, some sellers state in their listing that they only ship on Monday, Wednesday and Friday in order to streamline their shipping processes and save time.
What does take time initially is finding a product to sell that works for you. This is trial and error and is probably the most time-consuming aspect.
If you are selling on eBay, it will take time to learn how to best promote your listings. A website of your own will require time spent on advertising, driving traffic and maintenance.
But there is heaps of excellent advice on the forum. Asking questions as you go is a big help too, many of us have already faced the same problems and will be able to help you out.
Good luck and hope to hear more from you in the future :)