I have these comments about your planned isometric chest squeeze exercise.
If you are planning on using maximum contraction, which I suggest, make your contractions about 7-12 seconds in duration. Remember to breathe and not hold your breath, and to breathe deeply during your recovery period. I suggest 3 sets at the trunk-level position, 3 sets at the chest-level position and 3 sets at the eye-level position.
Now an interesting variation, one that doesn't use maximum contraction is what is known as aerobic isometrics. I like doing these with a basketball or medicine ball in hand. You perform these with about 35-40% of maximum contraction effort, again remembering to breathe, for an extended duration such as 2-3 minutes, changing your hold level from trunk to eye-level every minute or so.
I suggest you consider doing the chest workout in my article exactly as prescribed for your day #1 experiment. I've actually done that workout after playing around with it and believe it has the correct amount of reps. For best result, I also encourage you to do the Atlas pushups between chairs, benches or steps and go really deep in a slow and controlled manner like gymgirl did in the video clips. Doing them this way really works the pecs and sets them up for the maximum contraction isometrics.
This workout takes some time so I'd save the pullups for a different day, but I would conclude with some ab/core work, either some ab plank holds for time or some
hanging leg raises, hanging from a pullup bar and performing double leg raises until your feet touch the pullup bar.
Hang in there and be flexible as you explore the world of bodyweight-only training. And be careful with the
higher volume as your body does need some time to adjust to it.
I'll be following what you are doing.