This is just from my own personal experience and what I've seen on the trail, but if you have to start off piece by piece, I would suggest protecting the fuel tank first. That's the softest thing under there, and can get cracked easier than your pumpkin, or your oil pan.
If you’re starting off from scratch I would have to say tires. You can get to plenty of places without a lift, or skid plates, but street tires may not cut it. If you need or want to do a lift I would do the lift, then go for tires. After that it’s whatever you want or feel like. Navigation, Communications, etc. ect.. We will be more than happy to help you spend your money. Just have fun with it.
GOOD AT or Mud tires should be the priority. In terms of armor, the Fuel Tank and Transfer Case are my suggestion. Followed by the Shocks and anything that hangs at the same height or lower than the shocks. Lift kit will help but depending on what you are planning on doing, it could wait a bit. Rock sliders if big rocks are expected (side steps are not rock sliders). Front bumper & Headlight protection are important but again, depends on how deep you want to go.
Before I got into overlanding I used to live in areas where rock crawling and mudding were big events. Learned a lot from some competitors and home fabricators (also A LOT of what not to do). Pretty cool how a lot of those tricks and preps can help with overland builds.
My wife has a 2018 4runner pro. Stock it comes with a nice front skid plate and the gas tank is pretty beefy. The first think we did for was sliders (Not steps). My Tundra came with steps and I F'd them up first time off road. I replaced with sliders. A few of my friends have since bought trucks and installed steps instead of sliders (against my recommendations) and all of them have destroyed their steps and this is in the desert not rock crawling. Catch a rock the wrong way and you'll kill one of your doors.
Before I started throwing a lot of armor on your rig, really consider if you definitely need it, depending on the trails you intend to go on. You have to consider the weight penalty you will have that may force a suspension upgrade if you get too crazy.
I'm fully armored and with moderate gear (no RTT or refrigerator) I'm running 900lbs over GVWR fully loaded, which required upgrading the suspension to support it. Weight adds up quickly.
My Tundra came with steps and I F'd them up first time off road. I replaced with sliders. A few of my friends have since bought trucks and installed steps instead of sliders (against my recommendations) and all of them have destroyed their steps and this is in the desert not rock crawling. Catch a rock the wrong way and you'll kill one of your doors.
Would any of those vehicles have had enough clearance had they NOT had steps or sliders? It seems sliders are universally recommended even though they do reduce clearance relative to not having anything. In my area, big boulders are not common.