1. Yes, GVWR on the Tacoma isn't very high. I know people exceed the ratings all the time and it's very difficult not to.
2. My previous truck was a 1991 XtraCab and it had a very similar GVWR but the curb weight was something like 400 lbs less. So the effective payload was something like 1,600 lbs. I didn't have to really worry about overloading the truck to the point of frame issues or being unable to brake and handle. It was also a 22R-E which really was the limiting factor. You could safely load the thing without worrying about failure because if you did exceed the payload it wasn't going to move anyway.
3. With this Tacoma I have a GVWR on the plate of 5,350 lbs and that leaves me an effective payload of 1,385 lbs. So with a passenger, full tank of fuel, bolt-on sliders and fiberglass topper I'm left with about 620 lbs of payload. I added an ARB bumper, second battery and eventually a winch, this consumes about 185 lbs, so I'm down to 437 lbs of payload. With a simple rear bumper, 10 gallons of water, tools, recovery gear, Hi-Lift, shovel I'm looking at 145 lbs. That's going to be the fridge, food, clothes, a couple of bicycles. That's it. No capacity left for heavy skid plates, extra fuel, swing outs, RTT, etc.
4. I'm not saying it's not possible to put on 700 lb coils and OME EL091 Hilux rear springs. It might let us bolt on all the farkle and carry everything but the truck is overweight by 500 lbs. What that means I think ultimately is that it's going to wear out faster (as you're finding with coils) and the frames on the Tacoma are already fairly undersized IMHO. I'm also a throw-back in that I bought this truck expecting to keep it 25 years like that last one, which is probably no longer realistic.
5. My argument is that modifications need to be done with all the information available. You guys doing 700 lb coils I believe have gone pretty far overweight and should be considering a Tundra, F-series, Silverado, etc. to carry everything. Or if the truck is supposed to be a rock crawler with all the protection then it might not be a good choice for overland travel with all the gear. In the rest of the world the Hilux can do 1,800 lbs and there's the Cruisers for people who want to build out heavily loaded trucks.
6. I 100% think there's a hole in the Toyota models for a smaller truck capable of doing actual work like this. They used to be more rugged and I think people assume they still are, but I'm not sure that's true. We also don't know since the frames on the things rust out before they get old enough to know. So, yeah, things like a coil buckets, lower arms, spring hangers might start to fatigue. The back half of the frames on our trucks just seems so wimpy.