Where to begin?

That is one way to do it, yes.

A few suggestions:

For history – group the K, 2, and 4 kids into the same books  (grade 1-3).  Group the 7, 9, 11th into the same books (grade 7-9) unless the 11th grader is really passionate about history and wants to read the higher level books.

For science – again, I’m a big fan of grouping where you can, so all elementary kids go together.  Older 3 it is up to you and what you’ve already done with each one.

For Math – well, yeah, pretty much have to have each in their own math. Sometimes two kids can be at the same level (I have kids 13 months apart who are, but the rest of my kids aren’t).  Sorry!

For enrichment studies – you don’t have to buy anything.  You can, SCM has some lovely products like the picture study portfolios, but you can use any pictures, poems, etc you have on hand or can access through your library or online (aka Free).

For language arts – you can purchase things in many places, depending on what you want.  We don’t purchase ‘literature guides’ generally, we read the books and the kids narrate or we discuss (socratic discussion).  I do use Spelling Wisdom from SCM and make it double for copywork, spelling, and prepared dictation for anyone over 3rd grade.  (1 purchase works for all the kids).  We happen to use some of the Brave Writer materials, there are many writing programs or guides available for free or purchase.  You get the idea.

Hope this helps some!  Feel free to ask more questions!

I totally agree with Tristan on grouping them together with the books!  That will save you money since you won’t need quite as many books.  I plan on combining my 1st & 4th graders with the 1-3 grade books for the coming year.  Karen’s idea of using the library and buying used is great too!  I buy many of their books used from Amazon and Thrift Books.  Others we get from the library.  We have a great ILL system at our library which really helps!  If you belong to a homeschool co-op, they may have a library as well.

For grammar, Our Mother Tongue can be used for grades 4 and up.  It’s a 1-2 year long overview of grammar and all they really need.  It’s also very inexpensive and non-consumable.

For enrichment, you can cover this for free if you choose!  There are tons of great resources online or at your library.  You can add an inexpensive poetry book (or just use ones from the Public Domain).  Music can be found on Youtube.  I can google to find any artistic print and information on the artist.  Ambleside Online has lots of free resources too.  This can also be an area to be easily overwhelmed.  You don’t have to complete all the enrichment subjects each year, and especially not in your first year!  Maybe pick one or two enrichment areas to focus on at first.

For math, your younger DC can get buy with some manipulatives and inexpensive workbooks or older texts.  Strayer-Upton is very inexpensive and goes through 8th grade (I think).  The SCM Mathematics DVD has some great ideas on it too!  I would budget more here for your older DC.

For science, we have always worked together.  My 9th grader will be venturing on her own a bit this year.  There are lots of science options that will work for combining your younger ones.  Many of the SCM science programs work well as a group study.