What's your current height, weight, and general fat level (a description is fine - pudgy, muffin top, moobs, some ab definition, etc.)?
Dan John loves the ab wheel. I hate it and strained my abs using it. Use whatever exercise allows you to work in the target rep range, but be aware that using heavy loads can quickly take the abs out of the "weighted ab exercise" and turn it into a different movement. Think about how heavy a 6-7RM decline crunch would be, and the associated stress on the low back.
From the article, "Never plan or worry about the weight or the load. Always stay within yourself and go heavy "naturally." So, you should be able to get every rep on every set without grinding. use whatever weight allows that, and adjust as needed.
I think you should focus on doing one thing at a time. The 40-day plan is a high frequency strength-focused program. PLP is a high frequency bodyweight program designed to supplement more traditional training. I don't know why you'd be doing treadmill sprints. Figure out your specific goal (and I'll pre-emptively say that, "get stronger and drop fat" isn't a specific goal) and stick with the program best designed for it.