Spies that the main villain who had extensive knowledge of how Wakanda works said could help revolutionize the entire world. Why would he lie when it was his plan to put them to work?
But let's use your logic. Your entire thesis is based on Wakanda suddenly being found by tech that is decades if not a century or more behind Wakandan tech(so they can't find them through technological means).
By T'Challa screwing up and just revealing the location.
Wakanda never waged war on anyone so no governments had any real reason to invade their country and they were apart of the U.N. I doubt the U.N. was going to approve of other nations trying to invade Wakanda for reasons.
None, as Wakanda doesn't have Hellicarriers. It is however a massive city behind a 100% effective cloak. See the hellicarriers have "reflective paneling" that makes them invisible to an extent from a certain distance below them. Wakanda's is so good you could walk right up to it and not know it's there.
You realize the "Country" of Wakanda that the world sees is a third world fake, right? The entire world thinks they're and I quote, "A third world country of farmers and textilers". Even if they invade Wakanda, they wouldn't get near the city. They'd just find a bunch of huts and regular buildings outside the forcefield.
Tony and Cap spoke about Wakanda and the vibranium within it as if they knew more than the others as far back as Age of Ultron so at the very least Tony, his dad and Cap; possibly Nick Fury knew more about Wakanda than most but even they weren't aware of the Black Panther.
Having said that, with SHIELDs backing I think the armies of the world would be a pretty tough challenge for Waknada, remember that SHIELD and the US army had access to Stark tech which is no slouch weaponry in its own right; enough to cause the Hulk a bit of trouble so yeah, Wakanda isn't getting past Earths defences without a very good fight.