Melessa, I'm also trying to sort it all out as I go along so while I have no BTDT experiences to share, I have been thinking about this a lot.
If exposure to new concepts is your purpose, then I personally wouldn't worry about following an orthodox scope and sequence as long as your DS is enjoying the learning process.
If home ends up being his main place of math instruction because of homeschooling or afterschooling, then it becomes a whole different story but I'm not sure if you're heading down that road right now.
My plan for DD if we go homeschooling route is to get her through SM while supplementing it with both Montessori math materials and other "fun" resources like Beast Academy and iPad apps. I tend to lean towards unschooling side of things in general but when it comes to math, I like to know where we're going and how we're getting there.
