I would love to help you!
Find a good draftsman (or building designer) that understands building costs as well as good layouts that work. Stairs are alway a pain as they take up a lot of room, much more than most people realise. Going out is usually cheaper than going up, but site coverage needs to be kept in mind. This is something a lot of people don't realise either.
Tell the designer what you need but leave it up to them to work it out. That's their expertise and they know the local council by-laws, NCC/BCA, State Planning, etc.. They will probably even have a basic design idea already once they're on site and speaking with you!! The key is finding good ones........
6-8 weeks is around the standard time it takes council to approve it all. If you haven't heard anything within two weeks it's a good sign it's all good, happy days!
Extending is still cheaper in most cases rather than demolish. Unless the grand plan is very grand! Good luck with your project, exciting times ahead with many decisions you haven't even thought of yet. Tiles, colours, architrave choices......soft furnishings........
Michele, if you have plans or even something you've done roughly on the back of an envelope you can use this estimator to get a sense of your required budget. Check out
Online Renovation Costs Calculator
Good luck. Richard@themakeovergroup