Agree, Coral Connections for something custom like you are thinking. Was not a fan of Rick's. I am a fan of Aquatic Specialties, but they do not do custom builds and their store is pretty much around how they setup tanks they maintain.
Also, being in Luling, you could try Coral Fever, which is closer to you than it is to most of us. I know the shop took damage and did re-open from the storm, but I don't know if Seth does AIO custom work like you are looking for.
What tank size you have in mind? Something larger than a 55 gives a pretty wide range of possibilities

. For an AIO larger than 55gal in show space, I would think you need to be minimum 24" front to back just to fit the equipment and still have an equivalent 55 in the front, something like a 120g. That is a lot of space in the back, but would give you a 10"x44" sump and could include a built in ATO reservoir and even built in 2-part or 3-part dosing system if planned right. You would need to use space-saver style skimmers.
Another option would be to go to a 5-ft or even 6-ft length tank, and then partition of one end instead of the back, making more of a peninsula style tank. The sump area would be more square shaped and would better handle larger skimmers, but ATO and chemicals would be underneath.
Just a couple of ideas...