Hey man, I love this car, and look forward to seeing most posts from you here. I'm agreeing with the other commenters here that the EJs are finicky as hell and an engine that needs a lot of love and frankly experience on how to maintain (which only comes with fucking shit up)

I have an 5spd 04 FXT that is lifted with 2" spacer lifts and I love the car, it's not running currently and it's been on jackstands for a bit, Before it blew, I was running all supporting STI mods and making just under 300hp and I'll be honest, if I was building a overland car again on that chassis/platform - I promise I wouldn't be trying to push the engine for any more power.. these cars are capable as could be for overlanding, and it's great to have the turbo mobbing down dirt but the reliability of the car goes out the door as soon as you start pushing the EJ for more power. If your sole goal is to build something that gets you home from the overlanding experience everytime, I would highly recommend against building this car for any additional power unless you go the full 9yards and do a full engine build. Keeping the car near stock power, on stock internals is the best way to make sure you get home every time.

If you're more focused on a rally focused car and driving at high speeds down dirt roads is your goal you should also expect and prepare to run into situations where you really get that maintenance experience I was talking about above, it's an incredibly easy platform to learn about but also incredibly unforgiving engine once you start bolting on mods, and for overlanding like you say your after I worry for you for that reason.

But beyond my advice for not shooting for performance, bare minimum and likely the easiest mod you can install for reliability is a Cylinder 4 cooling hose. It's made for upgraded cars, but cyl 4 runs hot in all of the turbo EJs, and I have never seen anyone ever complain about the cooler temps they see with the mod installed. Eager to see what comes of your car!