G'day Warmbrak, rgmwa has pretty well covered it. Access to controlled airspace requires a PPL or higher (there isn't a "controlled airspace endorsement" as such - it comes with your PPL). RAAus were working on getting access for RAAus pilots to controlled airspace after appropriate training and endorsement, but CASA have said that the existing arrangements are satisfactory and don't currently intend to proceed with the proposal.
If piloted by a PPL holder, either RAA or VH aircraft can access controlled airspace. If a PPL holder is piloting an RAA aircraft, he/she must hold an RAAus licence as well, entitling them to fly that aircraft. A RAAus aircraft must have have VHF radio and transponder, the latter must be checked and signed off for correct operation by a LAME, and the engine must be on the CASA list of acceptable engines. Rotax and Jabiru are. There are no two strokes on the list.
A group build would be a brilliant idea for a like-minded, co-located group. Perhaps you could gauge interest by a post on another Forum thread?
Cheers, Denmit