I saw your post this past week and made a mental note to come back on the weekend with a reply.
What subjects does it include?
You'll be able to find the subjects broken down by grade on Calvert's curriculum page.
Do you do every subject every day?
Not always, especially in the beginning. We've been with Calvert for 7 years, and every time we start a new grade, we find we need to break the days in half until we get up to speed. A few weeks into it, we're comfortable doing an entire lesson a day. You can adjust the lesson plan any way you'd like, and we've done that too...getting 2 days worth of Math, Science and Geography out of the way on a Monday, leaving the slightly easier subjects for Tuesday (when my daughter has choir).
Does it lay it out well for the parent to teach it? Yes. Calvert spells out each lesson.
Does it leave room to add other subjects or things from other curriculums? (Like Bible)
I think it depends on a few variables, like how long it takes a child to get through the basic lesson plan, how busy you are with other activities in your life, and how much time other subjects would require. To add to the fun, sometimes the lesson plan itself varies in intensity. We have days where the kids blow right through their lessons, leaving a nice 2 hour window open. Then we have days where the basic lesson plan, all by itself, will take us until 3pm (those aren't fun). I personally don't add much else, with cursive for my 10 year old being the exception.
For the Calvert option, are you considered a private school teacher and an extension of Calvert School as a home educator?
The title of "private school" depends on your state. Here in Illinois, all homeschools are considered private. Regarding Calvert specifically, I do consider myself an extension of Calvert, and when asked where the kids attend school, I always answer "Calvert."
Is this curriculum affordable especially when you have more than 1 child?
I only have 2, and my husband makes a good living, so the tuition isn't a hardship for us (especially if your only alternative would be an area private school). However, it is considered one of the more expensive curricula. To decide if the expense would be worth it, you'd have to sit down and figure out how much your alternatives would cost (and as was pointed out by the previous poster, you should consider lunches, clothing, transportation, etc.), and then compare them to Calvert. Again, for us, 2K a year isn't bad. But 2 or 3K a year on a salary of $40K might be tough.
Also it talked about 2 different options for kindergarten. Could someone explain that to me??? I wish I could, but we've been out of K for a while now. I'm clueless!
Also could some parents tell me what you just love about this curriculum?
I love how comprehensive the curriculum is, as I would not enjoy having to pull together my own stuff, nor would I have been able to put together such a sophisticated program. I also love the ATS feature, since it not only provides support and feedback, but official transcripts as well. That they provides tests both with and without ATS is a plus, as I think it's important for my kids to learn how to take tests. Customer support is fantastic too.
What are some of the negatives?
Some subjects are terribly dry. I try to modify these by finding additional sources that convey the information in a more interesting way, using websites and books from our library. There are also times when I chuck the entire book for a subject and do my own thing, which you can do if you aren't enrolled in ATS. (I did this for 3rd grade History with my second daughter. We found Famous Americans painfully boring.)
I also question the emphasis on what appear to be minor details on tests. For example, I'd rather my 13 y/o daughter know the basics of a country...perhaps the general political history, the general geography, the major religions, the language, and how they interact with the world today. Therefore, I am disappointed when the Geography test asks a question about a minor resource the country provides. To me, that's specific information one would learn if one was focusing specifically on that country for either a test or a research paper, NOT something you should remember when you're covering many countries over 20 lessons. That kind of nit picky stuff irritates both me and my daughter, and I worry it will turn her off the subject itself.
Ah well...can't have everything.