Thanks everyone for your input! And James, it's fine, we can't expect you to do everything for us!
I saw that setup with the shelving, and thought about it while I was at Target.... I'd have to mount it on the sides, since the headliner isn't useful for supporting anything, and I'd like to not alter the roof. It does look like an awesome idea though. That, combined with a cargo net mounted on the liftgate should give me some nice supplemental space. And gotta remember to put an LED work light up there for cooking.
I did think about using the existing tie-down holes, and will almost certainly try that approach, since I'm all about using existing holes rather than creating new ones. I'll probably be creating my supports around the hole locations now, so more precise measuring is needed I suppose (or just a lot of cardboard for mockups).
As far as the tool situation goes... I'm currently using one toolbox for all my tools, but it's near its limit. I'm with you on the metal toolbox, and I think I'll just be using the plastic one I currently have for sockets, wrenches, and common tools like screwdrivers, hammers, and electrical things. I'll probably put the other stuff in another toolbox, since it's not used nearly as often, and it's almost exclusive to automotive use (gear pullers and the like).
In regards to rear seating, I was simply referring to being able to sit and chill in the back when stopped and not completely unpacked. I'm thinking I'll use two small drawers on each side for holding the small stuff, and then have a removable shelf in the center or simply use it for my aquatainer storage, since those are easy to remove and put back (though they're pretty heavy). That'll also solve the floor storage access problem, even if I end up having to modify the lid for clearance or remove it completely.
Rear seats need to stay the way they are, since I have nowhere to put a spare rear seat, and I'm not going to sell or toss it, since I want to be able to return the truck to mostly stock at least. That, and the solo rear seat covers up and stores my pump and hoses for my water system at the moment.
I'll look into removing those rear head rests though. My passengers never like using them anyways, so they're just useless...
The only thing I'm worried about with the inverter is adequate cooling. I'm probably not going to end up using it too much, but I'm all-too-aware how hot it can get on desert trips (hot enough to overheat inverters in normal cabin areas).
My kitchen counter may necessitate a "mini hitchgate" that mounts inside the cargo area just between the drawers and liftgate, but I've also thought of a novel way that uses a hinged panel under each drawer which can be unfolded and secured by cables w/turnbuckles... I'll have to see how that pans out, and may have to go with only one drawer on each side and possibly increase the height of the whole unit. Come to think of it, I'll have to increase the height for the aquatainers anyways, unless I want to make a cutout for them... hmmm decisions decisions...
As far as the second level, it's definitely for the soft stuff, like chairs, tents, sleeping bags, etc. This may change when I get the roof rack, but I'll probably keep the sleeping stuff in the truck so it stays dry for sure. It'll all be held down with those wonderful ratchet straps, hooking into a plethora of hooks on top of the drawer assembly. I'll also be installing a cargo divider mounted to the roof and to the drawer assy. to keep the cargo out of the passenger compartment and to keep my curious German Shepherd out of the cargo compartment
I think I'm going to heed your advice and mount the fridge on top of the driver-side drawer. Then, I can mount the action-packer on the passenger side. Center is for whatever else/laptop bag. Now I have to measure things and crunch numbers to make it all fit
And as far as gun laws, if it's stored anywhere out of sight either loaded or right next to its ammo, it's a concealed weapon... 's okay though, cuz I'm getting my CCW permit as soon as our new sheriff is elected. Then it'll just be a Service Springfield XD45