I haven't had my 4Runner for very long, but I'm slowly modifying it. It is an ORP and everything you listed there is exactly what I have on my list of things to do to it: RCI aluminum skids including the gas tank skid, RCI sliders, and Fox 2.5 with a 2" lift.
The only thing different on that list was that I was going to go with 265/70/17 AT tires, I figured sticking with the OEM size would simplify things. I do want to switch to lighter weight wheels eventually.
My only question to you is: you said no steel bumper. I have been going back and forth on installing a winch. When looking into them and everything involved, I've came to the conclusion that a hybrid steel bumper would be the best way to mount a winch.
I have been looking at the LFD hybrid steel bumper since it leaves the winch pretty accessible. Is there some other way to install a winch without going with a steel bumper?
I did see the hidden winch mount options too, and I do like that they save some weight vs the hybrid steel bumpers. The only downside I keep seeing mentioned though is that you don't have easy access to the winch that way.
Also, I do know that there are aluminum front bumper options, but I think if I'm going to go through the work and money of replacing the OEM front end I might as well get the added protection of steel at the front.
I think I'd start by saying that there's really no perfect answer for everyone. Everything is a bit of a balancing act. I just generally see a lot of stuff bolted on for style that doesn't offer much or anything in terms of performance benefits. And often significantly degrade the highway performance. Anything that adds weight or wind resistance will degrade performance. And they all add up. So it's worth taking a hard look at whether the things really help or not and if the benefit outweighs the costs.
I think the partial steel bumpers are a pretty decent compromise for a lot of people. And even full steel bumpers probably make sense for some people where they are doing a lot of offroading where they would be doing a lot of damage to the plastic bumpers. I've just found that most of the time the plastic bumpers are just fine - especially the front bumper. The front lower center does drag in places. The front sides have enough clearance in OEM form to clear anything I've ever come across. And by cutting them high you expose a lot of the parts to road debris and offroad damage that would otherwise be protected.
If I were using it on a ranch for a ranch truck that I'd rarely be using out on a highway, I'd probably want a big heavy steel bumper on both ends so I could use it to push things around without worrying about it. Much like how I'd normally have a flatbed and a big bull bar on a HD truck. Sometime it's more like bumper cars around a farm or ranch.
For a vehicle I'm going to take long road trips and explore up to moderate to maybe 6-7 type trails like the rubicon or poison spider/gold bar rim being sort of the limit - for that type of use, I prefer lower road noise for the 700 mile drive to the trail. And I prefer the lighter weight on the trails and on the highway. Not to mention that it's also a lot cheaper to keep the OEM bumpers - or even replace them a few times.
On the rear bumper - I don't know why you'd want to move the spare tire up to the bumper when there's a perfectly good spot for it underneath unless you're out desert racing where you're going to be burning through multiple tires per day for example. And not at the expense of 200 or 300 lbs. For me that doesn't make much sense. Not for a mulit-use vehicle that I also want to frequently access the rear cargo area and infrequently access the spare tire. Only once in 7 years did I have a flat tire. And my 34" tires still fit underneath. But someone who is going through tires regularly might find that they need 2 spares and/or want it hanging off the back instead.
For me - I found that it was as capable as I think I needed it to be and made the best compromise for daily driver and adventure vehicle to have a rear bumper protection skid and front hidden winch. I don't think I would have survived without good underbelly skids.
In my perfect world - I would have absolutely LOVED to have something like AHC from lexus. The biggest compromise that I think exist on the 5th gen is the trade between highway and offroad ride heights. I adjusted mine at least a dozen times in 7 years, had multiple iterations of air springs, coils with air helpers, spacers with light weight springs, and adjustments up front. And I never found something that was great for everything. Even just for offroad use. Above around 1.5-2" lift height and you lose articulation and the higher speed and general trail duty along with highway ride. But you give up ground clearance. And with only 33 or 34" tires, that's a problem on the more technical end of the trails I'd like to do.
Rear air is easy enough to make adjustable height. Front suspension is not so easy. I tried to find someone to build me an air spring that will fit over a fox 2.5 shock body. None of the major air spring makers would build something like that. I'd love to have something like the lexus LX. But I'd also want to keep the ride and performance of higher end shocks. So my last thought on the idea was to use a secondary shock hoop setup in the front and then run a fox air shock along with the coilover, but I'd remove the valving from the airshock, so it would only exist as a spring.
Anyway, suspension is a tricky issue to find something adjustable. But I seem to find around 2" height is where it works best all around.