What a good discussion!

I will say that we have only done Singapore math the way it is planned in the HOD guides, with nothing extra other than some flashcards in the summer. My dc have retained what they've learned very well - even after a 3 month break in the summer. They have also tested at the 99th percentile in math year after year on standardized tests. My advice would be to do the HOD hands-on plans for Earlybird K and 1A/1B, and 2A/2B. Then, do the Textbooks/Workbooks as mapped out in the daily plans/Appendix, not doubling up anything (unless you had a special situation of an older child beginning Singapore later).
If your child begins to struggle with something, I'd slow it down and do the hands-on for 2 days instead of 1 in the younger guides. If your child begins to struggle with older guides, I'd weigh if they are supposed to have mastered the concept or if they need time to grow into it before thinking I needed to slow down. There is much more practice and review scheduled in the older Singapore Textbooks/Workbooks!!! I do not grade assignments until around 4A/4B (and on up) and then, I usually only grade practices and reviews - unless they've spent quite a few days on a concept, in which case they should have it down and a grade should then be assigned.
Singapore Math was brought to the United States because it proved itself with outstanding standardized test scores, ranking best among math programs worldwide. We then felt we needed to "Americanize" it by adding more and more and more to it. I think that before adding anything, I'd really try it the way HOD has written in it. What if you can achieve outstanding results without all the extra - isn't that worth a whirl?

You can always add more, but until it really becomes obvious more is needed, why not enjoy doing less while still accomplishing so much?

I am not saying it is necessarily wrong to add more, I'm just saying it often is really not necessary.

My dc both LOVE math. I know in part it is due to it is short.

I know many dc hate math. I know in part it is due to it is long.

This is just something to watch out for IMO, especially as dc get older!

Math need not take forever if it is written well. And Singapore is! HTH as each family considers what is best for their needs, here also are some previous posts to peruse if anyone wants more dialogue on this...
Singapore Math (why Carrie picked it and my top reasons for using it)
viewtopic.php?f=6&t=4271&p=31537#p31537
viewtopic.php?f=10&t=112
Singapore Math – should I get the Home Instructor’s Guides or additional components?
viewtopic.php?f=6&t=4896&p=35879#p35879
viewtopic.php?f=6&t=6698&p=48902#p48902
In Christ,
Julie