There are several curriculums that you could use for Multilevel teaching but if I were starting out again I would go with Tapestry of Grace and get the paper units. Good resale price, excellent curriculum and fun:) MFW is great but you dont really combine until 2nd grade. Kindergarten and 1st grade a separate. I have used and enjoy both. We have also done Sonlight mulit age format and I didnt think it worked well without lots of tweeking.
One of the best speakers I have heard on multi level teaching is Heidi St. John. She talks about teaching Bible, History and Science together and teaching to each childs level. You start everyone together on the bus and as you reach that childs destination you let them off the bus. So your kindergartener would get off after the reading and color, the 3rd grader would listen and do copywork, the 6th grader would listen read an additional book and write a summary etc.
HTH