One of the places you need to go is here:
yahoo groups : search groups : secular homeschool
((sorry, my password is acting up or I'd give you the link))
It's a hugely active board of secular homeschoolers (about 500 actively posting members, several thousand who only post occasionally / mostly read). It's mostly US, but there are some kiwi/aussie/canadians/etc. on there as well.
There are also several "Common mistakes to avoid when setting up a Co-op" pages online that are worth reading.
From experience... setting up a co-op is about 40 times more work than simply homeschooling, and that's ONLY if parents are teaching. Once you bring in outside educators, then you've got tax issues. More than a handful of kids on any kind of private property and you've got insurance issues. Taxes and insurance are the least of your worries, however, because the BIGGEST pitfall are other parents. Homeschoolers are an independent lot... getting a group of us together all doing the same thing is rather like herding cats.
Don't get me wrong, it CAN be done, and even done well... but it is HUGELY time consuming. On average, most people I know setting up a teaching co-op (there are lots and lots of play co-ops with parkdays, etc., which is waaaay less work... a simple email list does the job) spend about 80 hours a week on it ON TOP of educating their kids.
It's why so few exist, period, religious or otherwise. The workload is prohibitive. An established co-op, otoh, is STILL huge amount of work... but after 4 or 5 years they've got the kinks worked out. Most co-ops don't last a year. A 2 or 3 yo co-op... expect a lot of difficulty with it. It really takes awhile getting these things up and running smoothly... and by the time they're up and running smoothly... they're no different from a small private school. Fees to pay, policies to abide by, etc. Even if there were half a dozen secular co-ops in your area... you may not like them.
I'm not trying to be Debbie Downer, here, promise!
Just suggesting that you do quite a bit of reading on the subject, before starting, if you haven't already. If the idea of homeschooling sounds overwhelming, take a 2nd and 3rd serious look at what starting a co-op entails. It may be the PERFECT thing for you and your familiy, but it's about 40x the work of homeschooling on your own and signing up for outside classes.