Right…I’m with you on the importance of parallel and perpendicular planes. It just helped me work through the process to start with a level benchmark. Once I had that I used the carpenter’s square to get things perpendicular or parallel. The rest of your post looks pretty informative. Thanks!
OK. No more level talk.
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I’ll know tomorrow after I run the skimming with a 3/4" bit. I’ve already learned a bunch and appreciate the help you and others have provided. As for being lucky or not…if the skim comes out smooth (meaning the bit is perpendicular) I’ll just chalk it up to my approach using the “L” word. 
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Sorry, I couldn’t resist.
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As promised, below are a couple photos of a skimming run on MDF using a 3/4" bit. I suppose it’s hard to tell from the photos, but I don’t feel any ridges on the surface when running my fingernail in any direction. Is there more I need to do to assess this surface?
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Nope wouldn’t do that. I think you said it best earlier…“no worries we’re all aiming for the same target.”
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Thought I’d try skimming an aluminum bar with a 1/4" square end mill (see photo). It came out very smooth, almost like a mirror. The holes already existed. However, I felt a hint of some ridges on the sides in the Y direction. When I checked the spindle I found it to be off a small bit. I was able to straighten it up.
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