Since people seem to appreciate it here, I'll continue a bit:
1. Regarding shoes/floor surface for squats: if your flexibility is subpar, you may benefit from wearing shoes with heels, or holding a 10-lb weight in front of you. Both of these will move your center of gravity forward a bit, reducing the tendency to fall backwards. If the floor is squishy, like with training mats, your heels will sink in and raise your toes, tipping you backwards.
1.5. My best frogstand ever was on some training mats the other day, where my fingers could really dig in to the mat. I think maybe I'll build some small parallettes or get some pushup bars to see if I can do it a little better. Then I'll know that it is more a wrist flexibility issue than just a forearm strength issue for balancing.
2. Log your progress. It's such a slow program that it's hard to see progress from day to day, but looking back at my log, I've definitely improved over the past couple of years.
3. You probably will be better at some exercises than others. I have weak upper back (as mentioned above) and my grip isn't that great either. My grip endurance is holding me back on leg lifts, too, but I'm almost near the end of the pushup scale, and just need to do a little cleanup work on my raised leg for pistol squats (my lack of hamstring flexibility leads me to bend that leg). I know females that I train with that can do full bridges like nothing, and I can't get my arms straight on days when I do have the strength.
4. I thought about skipping some steps, especially in the pushups, but using the form and the tempo cues, I gained a lot from the early steps of pushups. I've had to add more sub-steps than I've been able to skip (though I'm not much a fan of the half- motions). I added half uneven squats (to a bench), TRX pistols, and weighted pistols (reducing weight over time) in order to get my pistol complete, though it's still not clean. I added what I call 3-point pushups (1-arm pushups with wide spread feet) and that's where I'm currently working, as I can't even do more than a couple clean controlled negatives with my feet together. There are probably others, but the principle of progressively more difficult exercises is the key.