We like MEP a lot too. I don’t think it takes a lot of prep work. I just grab my printouts and we go. I have a box of manipulatives that we use (I don’t worry if I don’t have exactly the “right” one, I just use what we have).
I have 3 kids in 3 different levels (ages 6, 8, 10). I’ve done it two ways depending on the day: sitting in the middle while they’re all working on it and going back and forth between the kids (not my favorite method, but it has worked). The other is to take them separately and work with them while the others are doing something else.
My olders often do it all by themselves (they don’t like to be interrupted) and then come to me at the end and we go through the non-workbook page stuff then. Sometimes one of my older kids will do the lesson with my youngest (they all like that a lot).
Yes, it is spiral. This style has really worked for us. There is repetition of concepts as well as variety to keep the interest. This method has really helped them to think about math as a whole and not segmented…but I know that there are other families who do not like the spiral method (hence the plethora of curriculums available!!)
As far as back-tracking: is there any way you can get your hands on any of the Miquon books? You might not start out at the first book, but maybe another book. If you can leaf through them, that would help. MEP is online so it is easy to see what concepts are taught, etc.
I hope my experience is helpful,
Tanya