I know it can seem overwhelming, but once you get into it, it gets easier.
Finding a local support group is a good idea.
Don't spend a ton of money on curriculum ... You may find this one or that isn't the best suited, and it's easier to change if you haven't invested a fortune. Many places have used curricula in local stores, through church groups, and don't forget eBay. The library is your friend. Even a poor public library is like gold, but one with a good base of parent/teacher books is invaluable. Check out interlibrary loan too ... Some places it is still free.
Especially if you are starting with younger children, just focus on the basics. Learning to read, know colors, counting and simple math concepts are easy to teach in a low-key, games kind of way.
You don't have to teach EVERY subject every day. I started out teaching reading, kindergarten math concepts, and just reading a lot of books. There are MANY great children's books out there that introduce science, history, etc. Experiment books that use simple materials are fun and teach resourcefulness as well as the topic they focus on, and keep kids interested. Biographies written to involve and interest kids in the lives of historical figures are great.
The nice thing about homeschooling (ONE of the nice things) is that you cam follow your child's interests. I started with the basics, then by 4th grade I was teaching web design, typing, foreign languages, creative writing, and all sorts of things my child WANTED to learn. Her handwriting wasn't the best, but I didn't make her spend hours practicing it. (I figured if nothing else, most things are entered by keyboard anyway!) But guess what? Within two years, her handwriting was perfectly fine anyway. And we never had to struggle over it.
Don't stress. I forget the figures, but a large percentage of classroom time is spent on management details -- lining up, changing classes, handing out paper, etc. You can accomplish much more instruction in a shorter time. So don't worry about falling behind. If you are diligent, you will end up ahead. It does take a while to develop what works for you, so don't worry about it in the beginning.
Relax, get support and resources and information, and have fun. Providing your children with one-on-one instruction by the person who knows them best certainly puts you ahead of a teacher struggling with 27 children.
(And btw, I teach school now, so I've been on both ends of it. I MUCH prefer smaller classes and one-on-one or small tutoring sessions!)