You address many of the reasons that the West Coast Gatherings and NEST have the rules that they do.
You also cover a known situation - there are fewer women who SHOW to these. You first have to get a core group together, and get past worrying about whether your potential next partner is there. Age doesn't matter when you're just trying to meet people "like you". If you do more, swell, but first, get it started.
THEN try to go past that point.
Your responses are true of all ages and nations who are shy about our interest. Getting into groups of us WILL change that for you. It's hard to feel odd about this when there's half dozen of you there. Harder still when there's a score of you. There are always a large group of PEOPLE who are shy about a deviancy like this. We're not garden-variety normal. We're a GROUP that's not such. When you see the group regularly, you don't much care that everyone ain't like this. You find what's good in it, share it with someone outside of this, and when someone outside of this responds well... you get the idea.
Do note that the ONLY way work will know is if you show them.
Do also note that you don't HAVE to tie someone. You CAN have them held, voluntarily, by several (one per arm, one across the upper thighs, for instance).
There are ALWAYS more men than women, with exceptions proving the rule. Occasionally there are events whose male-to-female ration is better than 2:1. That's INCREDIBLY rare. To wit - there have been over one hundred "gatherings" I know about, worldwide (hosted a fair bit of them myself). The ratio is nearly always higher than 2:1.
Having said that, I've hosted events that had a 4:1 ratio that were a blast, where there was tickling play that everyone enjoyed, 20-something to 50-something.
There are couples that come about from gatherings. There are MORE of us who get confident enough to find someone OUTSIDE the gathering with whom to partner. Gatherings serve many purposes in our community, locally and worldwide.
In response to your count:
1. Don't shoot for a headcount. Shoot for making a core group that gets along, and grow that to where it's near 20. The last West Coast Gathering in LA was near 20, but got bigger when people from other kinks joined in.
2. There will ALWAYS be more men than women. I will DELIGHT when this turns out to have changed. It hasn't. It's why we seek "converts" to our interest. Read enough here, and you'll find several women who didn't seek this originally, who got into it from a lover. They converted.
3. Location is by availability. If you have such a location as you describe, you're set. If you don't, do remember that they're not free, or gov't sponsored. Hosts do so in their own homes, or by getting a collection together to host in a hotel, or by hosting in a BDSM club.
The BDSM club CAN work for some, but WON'T work for all. Some are too shy for the strangeness of it.
4. Rules are ALWAYS good. I use a set. NEST uses a similar set. So do all gatherings in the US, and I believe the events started in England and Canada do likewise. I can resend them to folks there. There's a website of mine due for an update that has rules and such, interviews, etc. Folks following links in my signature will find such.
Caroo, ya raise good points. Hope you help these to grow in Australia. There's just too many people. Would be excellent if, next time I visited, I could spend a munch with y'all, drinkin' good brews in good company.
Hope these observations help you and others!