Every paint job is different, even if it's the same color on the same model. The history of your specific 4runner plays a role too. These trucks are getting up there in age so there's always the chance that it's been corrected or had some paint work in the past that you might not know about (unless you're the original owner of course.)
You really have to operate based on your specific vehicle. The only way to know how much clear you have to work with is to use a paint depth gauge or at least know a lot about the vehicle's history. Even then, I wouldn't suggest sanding it. It might be a common strategy in the body shop world, but keep in mind that aftermarket paint jobs tend to have a LOT more clear than most OEM ones.
You should only be sanding OEM paint if you have a ton of experience under your belt. We always tell the joke that the person doing all the sanding in the body shop is the lowest on the totem pole, while the person that does the sanding at the detail shop is at the highest level. OEM clear is paper thin (or less!) so you need to really know what you're doing if you're going to sand it.
It's not just about the grit of the paper. You could go through an edge with 5000 grit if you don't have the right feel and technique. It sounds like you're not looking to chase perfection for show car results, so a moderate compound/polish with a dual action polisher will be a much safer way to go. You can make your paint look amazing compared to all the other daily drivers in the parking lot, while retaining as much of your clear coat as possible.
Some of the top paint correction experts are able to level the orange peel out of OEM paint without removing too much but those guys are the best of the best. Another thing to consider: even if you were able to successfully sand your truck without going through the clear, how much is left in terms of protection afterward? Typically the deeper you dig into the clear, the softer and easier to scratch it becomes. Also, the majority of the UV protection migrates towards the top of the clear - so you can technically still have some clear coat left but you've removed most of it's UV protection.
I don't think sanding is a good idea in this case, but I'm all for giving it a nice paint correction. Happy to help if you have any questions!