I'm curious about things such as should I use plywood for the boxes of the cabinets since it gets pretty humid here in Central Arkansas, or should I go with solid woods throughout?
I'm really leaning towards ash because I want to stain it more along the lines of a Paul Reed Smith guitar than traditional kitchen cabinets.
You haven't asked specific questions about fabrication, so I'll just address what you've asked about. I wouldn't build the cabinets from solid wood for many reasons. I would use plywood. If your intent is to get an all wood look, melamine would be out because it's white (or tan) on the inside. For other plywoods like AC or AB, you have an inordinate interior finish, and like melamine, you would have to skin the outside with some other material.
Just as a note, decorative hardwood plywoods are graded with an alpha character for the face grade, and a numeric grade for the back. Plywoods graded otherwise are likely imports and/or structural/construction grades. There are parameters to pay attention to for what is designated for the quality of the core, and what constitutes the quality of the face and back veneers.
Not only are the faces and ends visible, but the underside of the upper cabinets are also. If you want to use Ash, for a plywood, I would use an Ash hardwood plywood, and use the lumber for other areas. You might consider making "frameless" cabinets, as there are many advantages to that design. If that interests you, I would be happy to list the advantages and disadvantages.
If you are going to fabricate the cabinets yourself, space does present an issue as you get into building the boxes, as they take up some room.