Why plan? Some of the truly epic bicycle rides (e.g. http://cyclingtotheashes.wordpress.com/ ) began with almost no planning at all. Just ride out the front gate and keep going. It's not really necessary.
For a shorter tour, though, I normally plan out the tour, at least in outline. It makes for a more pleasant journey. This is a very individual thing, so it's a process of trying things and finding what works for you.
How to get to the start/finish ?
Why not start from home? I live in an outer suburb of Melbourne, about 45km from the centre. I find this is the most dangerous place to ride. Australia generally is a very car dependent society. Almost all trips are taken by car. It's not comfortable or safe riding in these suburbs. I prefer to start and end bicycle tours at least 300km from a major city. That might seem extreme, but you have to get out of the city type zone. Where people either commute to the city or take day trips.
I mostly take Vline trains to the start and finish. It is best to use the stations at the end of the line. There are limited places for bicycles, and if your bike won't fit then you just have to wait for the next train. So you can be standing on the platform, train comes in, and the baggage car is already full. In some places there are only two trains a day, so the wait can be quite long. At the terminating station you can get there early and make sure your bike is on. There is plenty of time to load the bike.
Which roads to ride on?
We have a system of labelling roads. A,B and C. A roads are interstate highways. They typically have wide shoulders, so they are safe to ride on. It's not very pleasant though, with the traffic whizzing past you at 100km/hr. My preference is to ride on C roads, or even the minor roads below the "C" roads. Rail Trails are even better, no traffic at all. The B roads are especially difficult. Looking on the map it is hard to see how much traffic there is in a normal day. Some places have really heavy traffic before the start of work, and then nothing for the rest of the day.
Sometimes you will find a "C" road that runs parallel to an "A" road. These are great, because everyone in a car will take the highway, and hardly anybody will take the slow road.
Why be self-sufficient?
In 2000 I set off on my first long bicycle tour through Queensland. I set off from Brisbane, heading north. For breakfast, I like cereal (weetbix) and milk. I would stop in, or near a town, buy some milk before I stopped and use it in the morning. It was usually cool overnight, so the milk would not go off. Australians are now puzzling over this - as you go further and further north you are going to get to a point where there is 2, or 3 days ride between towns. No shop, no milk.
I learned to carry everything I need. Now I carry powdered milk, and mix it with water. A small thing, but it makes a big difference.
You can ride town to town, or even pub to pub (no need to carry a tent), everyone has their own style of riding.
The big advantage of being self-sufficient is simple. You can stop when you like. Once I was riding south from Swan Hill into a really strong headwind. After two days of pushing into the wind, I did my shortest day ever. At 10am in the morning after riding 30km I put the tent up and rested. Of course, when I woke up the next morning the wind had dropped, and it was easy.
How far to ride each day?
Until you feel tired, maybe. I find that I tend to press on, push too long. This is fine for a day or two, but then it stops being fun. There is also the effect of fitness, and age. Nowadays I find that I can ride 60km or so most days. So when planning a trip, I discount this and aim for an average of 50km. This allows for the really bad days when the rain and wind are in your face, or you are climbing many hundreds of metres. Another way to think of this is to take the longest day you have ever ridden fully loaded (110km in my case) and divide by two - that will be a sensible average.
How many days of food to carry?
Generally I will carry enough food for four days. This means that if I have a major mechanical failure that will take me a day to fix, that I still have enough food to get to the next town. Distances between towns in Australia can be quite long, even up to four days in the outback.
I tend to carry dehydrated food and water. I've met cyclists that never cook and just live on tinned food. For me, a hot meal makes me feel better, and the extra weight of the stove is worth it.
Where to camp?
Stealth camping is worthy of a whole article on its own. I actually use Google Street View a lot. Go to 60km on the route and click until I find a good spot. It's a bit of a luxury to know where you will be camping, but it is one less thing to worry about.