Get that cooling system as good as possible.
Yup. All the stuff you already did, plus check your hoses if you haven't already, and not just the big ones that go to the radiator--all the little ones, too. Maybe even carry spares, since they don't take up a lot of room, and they might be hard to find along the way. Viscous fan coupling working OK? Belts? Another easy spare to carry.
Anything else I should go through?
Think specifically about things that A: would put you out of commission if they failed, and B: you wouldn't be able to find at any NAPA or whatever. You'll have a support vehicle, so you're never likely to be more than an hour from an auto parts store or a mechanic of some kind.
Bring a Factory Service Manual and some tools. You'll probably never use any of it, but you'll sure be glad you have it if you do need it.
I would strongly recommend a good coolant temperature gauge.
This, yes. You don't mention if it's the factory gauge that's not working or an aftermarket one. If it's the factory one, it shouldn't be too hard to put right. Probably a faulty sender or wiring.
I'm planning on getting a turbo kit
Yes, a turbo will really wake up a 3B, but you don't want it
too awake. Moderate boost, and careful monitoring of engine conditions will serve you much better than maximum power if you want to maintain reliability. Remember, when Toyota made a turbo version of the 3B, they completely redesigned the motor, they didn't just add a turbo and go.
Definitely do it now, but keep doing it too.
Oh, HELL yes! ^^
If you're going through Nashville, TN--Prince's Hot Fried Chicken. Oh, man that sh*t is good! Damn spicy hot, though, so there's that.
Looks like you're planning Interstate 15 from Los Angeles to Las Vegas? I dunno, I haven't been on that road for a while, but from what I recall, folks drive really, really fast there. Might not be optimal for a 3B Troopy. Maybe detour up to Death Valley, which is an interesting destination anyway. Some pretty good trails there.
And on the way back home from Colorado, you can stop in Cawker City, Kansas. Home of the world's largest ball of twine. Really. lol
I've driven across this great land of ours, coast to coast, three times in 3B powered Troopies. Here's a list of everything that went wrong along the way:
-Not
-A
-Single
-Thing
Have a blast! I'm jealous.