I was part of a syndicate for a number of years. I’ll say up front, the most important aspect of choosing syndicate partners is to make sure that they are easy going people who aren’t afraid of spending money - the kind of people who say “you want it today? That’s ok. I’ll go tomorrow”, and “we need a new farnarkle for the sprugleplatz? Sure, how much do we need to add to the kitty?”. I was very lucky to find partners just like that.
As for organisation, we set up a Pty Ltd company that owned and registered the aircraft, with the 3 of us as directors (one of had to be specified as the maintenance manager). Primarily, that was to provide some legal protection for us, as in the case of one of us causing some major mishap, the aggrieved party could come after the company and its insurance policy, but not after the rest of us personally. From memory, it cost about $500 to set up the company, and the only overhead was that one of us (me) had to be the company secretary and file a report to ASIC once a year, and we had to have a ‘board meeting’ (ie I sent an email to the other two) where we agreed that we were not trading insolvent.
Send me a message if you want more details. It was 10-15 years ago, but I probably still have some records that I can dig up.