Ryan
Plan 5500 that way ATC know early (when your plan is submitted) that you want a clearance (apart from the fact that you have planned CG), request your clearance before you taxi at AF they may not give it to you due traffic inbound to Brisbane, if not request flight following at that time if you get flight following they (ATC) will give you a code which you will carry all the way, this will not be a clearance to enter controlled airspace (you will have to remain at 3500, I think that is the control step for that route) but you will get traffic separation (from IFR) and get told when to change frequencies you may also get told to contact centre on 119.5 for clearance but if not as soon as you get handed over to 119.5 request your clearance "Brisbane Centre, ABC, 25 miles north of Gold Coast maintaining 3500 request clearance as per flight planned track amended 3500 (your plan says 5500), you will get instructions from there, read back any changes to you flight plan such as altitudes, track changes and holding if required. CTA/CTR is easy they tell you what to do, you just have to do it and they keep you separated from all traffic.
Hope the flight goes well.
Allan