Hi justinjonesteach,
I was in the middle of answering your original post when I see you added a few other questions in subsequent posts in the thread.
I touched already on the ILD question, and I see you’ve settled on the 30 ILD D30 polyfoam core.
Regarding the 5" thickness, a 5"-6" polyfoam core is commonly used in the mattress industry, but the thickness of a mattress that is either “needed” or “preferred” would depend on the combinations of the layers and components that are needed to achieve the design goal of the mattress and provide the PPP (Pressure relief, Posture and alignment, and Personal preferences) that can best match each person and their unique body type, sleeping positions, and preferences. In the end, you won’t know if the comfort or thickness meets with your needs until you have the completed configuration at home and are able to personally test the completed combination.
As you’re creating your own DIY mattress, you may wish to read option 3 in post #15 here and the posts it links to (and option #1 and #2 as well) so that you have more realistic expectations and that you are comfortable with the learning curve, uncertainty, trial and error, or in some cases the higher costs that may be involved in the DIY process.
Phoenix