I wouldn't say there's anything major to be aware of. I guess if you are working on it be sure to use high temp silicone grease where there are rubber parts. Regular caliper grease might not be appropriate on the slide pins. But it is ok where the pads slide in the caliper. Do you know what is sticking? The slide pins, the piston, or both? I'm sure you could just rebuild it. You can get a kit that should have all the seals and rubber parts. I've not rebuilt rears yet, but I did do my fronts. Not hard, just a little messy. I'm guessing the kit would come with the square-cut seal (seals the piston inside the bore), the dust boot, a new dust boot retaining ring, and probably the dust boots for the slide pins... all for bother rear calipers.
Other things: Have a way to stop the brake fluid from leaking out of the line when you remove the caliper. Make sure the pads go in the correct way/correct side. Sounds dumb, but I'm sure it easy to overlook simple things. Pay attention to which slide pins went where. I don't think it matter on our trucks, but we used to have a Honda accord that had 2 slightly different style slide pins that had a specific spot (top or bottom). If they were in the wrong place, it would lead to uneven wear. Like I said, I don't think it's an issue on 4runners. I haven't messed with my rears in a while.
The thing to check is if the piston is frozen, is it pitted from corrosion. If so, you'll need a new piston. I had to replace 1 on each of my front brakes. The OEM is expensive. Here in the states I ordered some from rock auto and they were a perfect fit and looked identical. Must more cost effective. The rebuild kit should come with some pink silicone grease to put on the seals. It's a tiny little pouch. You might want a larger tube to keep on hand, but also the rear only has 1 piston, so maybe its not a big deal.
I say all this to say that replacing calipers, pads, and rotors is probably overkill. I will, however, give you great piece of mind that everything is fresh. If one side is frozen, the other side probably isn't far behind. A rebuild on both would be appropriate. If your rotors are within spec on the minimum thickness, they are likely fine unless there are weird vibrations or something indicating a warp (typically its due to overheated pads depositing too much material in one spot. Feels the same as a warp. More common on the fronts because they do more of the stopping) or some other uneven wear. If you have the time, you could take the rotors to a shop and have them turn them and ensure they're flat. Changing, though, is much easier.
A word to the wise based on my experience: If you do a rebuild, and decide to clean and soak the calipers in a metal rescue/ rust remover solution. You should repaint them after. I soaked mine and I apparently took off some kind of factory coating. They never rusted in 10+ years and 200k miles, now they're rusting. Not bad. A wire wheel will clean it all up. Maybe another soak for good measure, but that means taking them back off, tearing them down, cleaning... and then painting... to do it right. Kind of a hassle after the fact.
Not sure on other models besides the FJ using the same set up. Here, Tacomas have rear drums. Tundras might have rear disc, but they'll be larger and probably not fit. New gen 4runners, use the same size I think. There are threads of 5th gen "upgrades" for the 4th gen and people say they fit. I wouldn't call them much of an upgrade, just another potential part number that will work.
Here's a good, concise video on rebuilding. Of course there are tons of others too...
How to Rebuild a Brake Caliper or should you Replace it? - YouTube
