I'm new to formal afterschooling, too. At first, I felt like you do. I was completely overwhelmed by the quantity and quality of materials that it seems like other families are able to cover. Since obsessively stalking these boards, though, I've come to the conclusion that many of the lessons can be covered in just 10-15 minutes. Totally do-able.
Also, I've decided to focus on the basics for now (math and reading for my first grader) along with lots of opportunities to learn through field trips and just following her interests (e.g., a robin's nest outside our window has resulted in lots of reading about eggs, robins, poems with robins, etc.). Once the reading is rock solid (and it's above grade level now), I can direct her reading to more history, arts, etc. Between her school and my work, there are only so many hours in the day, so I need to just focus on what I think will make the most lasting impact.
As for math, I had the same questions as you. I (incorrectly, I think ) assumed she wasn't getting the proper foundation in PS so would have to start from scratch. I got Math Mammoth 1A and 1B a couple of weeks ago. Instead I should have done the placement test and bought just 1B. 1A is boring and babyish, and she doesn't need it and rebelled against doing it. In working with her on the lessons, I have been pleasantly surprised by the skills she has developed in school, including some mental math that I deduce from my reading on this board is taught as part of the Singapore Math curriculum. And this is achieved in a classroom that uses Everyday Math. We scrapped 1A and dove into 1B.