Hi Missy! I don't think I've "met" you before, so welcome!
I'll take a stab at some of your questions. I only know what I've found out as I'm ready to start Bigger with my oldest soon. I haven't used it yet.
After the gentle grammar in Beyond, HOD reccommends starting with R&S 2. As far as the R&S books lining up with "grade levels"...they are advanced, teach the concepts well, and I believe have finished all the grammar you'd need to know with their "grade 8" (final) book. I'm going to be using R&S 2 with my "3rd grader" this coming year.
I do believe that R&S is scheduled every day in the guides...not exactly sure if you do everything in the R&S book. I know for sure that HOD reccommends doing much of the work orally and only a bit of it written.
You are right that you won't need Igniting Your Writing. Carrie adds her own writing assignments in to Preparing. I don't know how old your kids are that you're looking for...I know of at least one mom that is doing Bigger with a 5th grader and is going to add in some of Igniting Your Writing for him as he needs more writing instruction than is in Bigger because he is older than the target age for it.
Hopefullly someone else can help you out, too.

Kathleen