The history of the MCU is whatever they decide it is. Why assume we know everything already? Stark didn't know about SHIELD in the first Iron Man movie, but it already existed. At the end of that movie Fury says something to Stark along the lines of "You think youre the only superhero out there?"
Not really. When you make the world look just like our world, you have created the expectation that it is just like our world except for the changes you show happen. If you break that unspoken agreement, it's like trying to retcon real life. They can't say "well, everyone on MCU Earth has two hearts," because that breaks the illusion, the contract, the premise. That's why, as far as we've seen, the MCU is like our world, and notably unlike 616 whenever that conflicts with Earth's actual history, and that's why we can expect them to continue to make that decision.
Are there secrets? Absolutely, Wakanda is highlighted at the end of Iron Man 2, but none of that gives the MCU the licence or motivation to throw audience expectations of the world they've created out the window.
Show, don't tell. That's what I'm saying.
Basically, its not enough for the audience to buy that a country of isolationist primitives with laser guns could exist. The audience may well believe its *possible*. . . but if they have zero *sympathy* for said country, you're stuck with them being antagonists at best. And a high tech nation deliberately living a primitive, unpleasant tribal life, except for the powers that be that enforce said existence via high tech weaponry ( and that is *exactly* what it would come off as )? Is the kind of thing that T'Challa would have to be actively ending, in order for him to come off as even vaguely heroic.
Speak that word, brotha!
I think a lot of the great stories come from T'Challa trying to balance his new ideas against the old ways. That's a story that resonates with everyone,in every society, and is a big part of BP's original mythos. T'Challa's conflict with Wakanda's old ways, and the problems he brings to their beliefs with all his tech, typified by Erik Killmonger, makes for a good story, and one of his greatest, if only for being one of the first comic book story arcs ever. I think calling back to that would be a great start, what with Killmonger being the closest he has to an arch enemy, to set up for that conflict in #2 after dealing with Klaw and some mercs and maybe M'Baka in #1. After that, there'd be a few different ways you could do things...
A thought on Priest's tech level: Did Priest make Wakanda a product of T'Challa or vice versa? Because by that time, T'Challa had been active long enough to have designed and invented Wakanda's military machine, satellites included, all by himself.