Renovation Brisbane - help needed, please...

Yep... I'm brand new to this site and forum, but from what I have seen so far it is brilliant!
Not sure if anyone can help, but my wife and I are in real need of some help/advice/anything! Situation as follows: We bought in Gordon Park, Brisbane, QLD, about 4 years ago. We really love where we are, but as our family is about to grow to 4 in November, it means we need a bigger place. We've looked at buying elsewhere, but can't seem to get away from the fact that we really love where we are right now. Hence, the decision to fully renovate. Looking at between $250k and $300k (possibly more if really required) to build in underneath, and also redo the top floor as its deisgn is not so good...
Here's my main problem... I work long hours and, put simply, building/renovating is as foreign to me as anything possibly could be. I've never had the need, desire, time nor motivation to do any renovations at anytime in my life to date. Until now. So what I'm looking for is to comission an architect or building designer to take control of everything from design stage right through to completion, whereby we can celebrate (hopefully) and crack open some champagne (or beer, preferably). I know this will cost me more, but I feel I need an expert to take control of this project, and spend our hard-earned money wisely.
So I guess what I am looking for is any advice that anyone might have. Anything at all, please! Traditionally I have relied alot in the past on referrals from people when buying any big-ticket items. Unfortunately I know no-one right now going through this, hence referrals are difficult to come by! Does anyone have anything they can possibly help me with? Doesn't matter how small you might think your advice is - I will greatly appreciate anything anyone can add, here. Positives, negatives, to do's, not to do's, architects or Building designers?, what to avoid, where to start?...anything at all...Thanks for any responses that might come back! Tom.