You do not need even the text book if you are using Carrie's activities within the (Beyond) guide (which you'd have to purchase separately - they'll honor their package pricing when you purchase the rest of the Beyond books next year).
OR
You can use the text (talk through the lesson until there's an arrow that indicates to go do an Exercise in the work book. With the second option you may need to work in some hands-on activities of your own.
That said, you do NOT need the Answer Key unless you want it - the math is simple enough in levels 1 and 2 that it's almost easier to check everything mentally than it is to find and check against the answer key (which lists only answers, not the question or solution). However, by Level 3 I have found that it is nice to have (multiple digit multiplication and DS and I are checking his work together at the end of each exercise), so getting it now is not a waste of money, IMO, though it may sit on the shelf for a year or two.
It is NOT included in HOD's package, but needs to be purchased separately.
You also do NOT need the HIG (Home Instructor's Guide). Of course, if you want to purchase it separately for ideas for hands-on activities (especially if not using the Beyond guide's math activities to match with 1A/B), then you can. I personally have not seen it to know if it is worth it at this age or not. Maybe someone else can chime in, but IMO, just what's offered by HOD has been enough. (We've just done one Exercise per day, sometimes talking through the Text first, sometimes not, with the goal of finishing 1A by around Unit 17 and 1B by the end of the year, not even really referencing the schedule in the Appendix except to check occasionally if we're on track to finish on time.
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Blessings,