Yay, I'm so glad! : D I got you covered, ask as many as you like! xDD
Riding horses at a basic level is pretty easy. Depending on what style you ride, it pretty much just comes down to personal coordination, and how agreeable your horse is. Most people who are old enough to have good coordination and are pretty fit and strong can pick it up in just a couple lessons. I'll describe it from an English standpoint, since the horses I ride are ore that than Western.
All you really have to know to ride a horse at a walk from one place to another is: steering, (pull right to go right, pull left to go left), telling a horse how to go forward, (squeeze with your legs or kick a little and tell them walk on), and stopping, (pull back with both reigns and say whoa or ho.) There's a lot more to riding than that, but if you are solid with all that, it'll get you from A to B :) This is what we teach our beginners, just a lot of steering and stopping and starting. If you're out on a trail, we might also teach a one-rein stop. If a horse panics and bolts, you are NOT going to be able to stop them by pulling both reins. But if you pull on just one, this forces them to circle, and that forces them to slow down :)
As for the other questions, you really have to ride a variety of horses before you can feel confident. Just because you can ride Mary-Beth doesn't mean you'll be able to ride Joe xD Joe might not be as forgiving as Mary-Beth, or maybe he's way faster, or slower. For me, after riding 8 years on all of our different horses, I've only recently gotten really comfortable just hopping on random horses and expecting them to behave for me. But that's because I'm ready for anything. I ride a lot of problem horses, and I've been trained to always be alert the first time, no matter what. Even if the horses are all okay being ridden generally, they all have their own minds and ticks ^^
And lastly, i think the tropes that annoy me the most are tireless horses, where they get treated like motorcycles, just ready to go at any time, and loyal horses that defend their owners to the death. Horses need a LOT of care, and they're really pretty delicate. If you don't warm them up properly, they could get hurt as you gallop away into the sunset, or if you don't cool them down after hard work, they can get really sick. And about the loyalty one, horses are herd animals, yes, but they only are that way because of the safety that offers – as in, if another horse is with me, they might be slower than me, and I'll survive. Unless they're specifically trained, a horse will run far away at the first sight of danger, unless their only option if to fight.
The last trope that really makes me mad is when people just drop their horses reins, or let them go off into the wilds with all their tack on. If a horse had a bit in its mouth and steps on its reins, it's going to hurt the horse, really bad. I see this most commonly in western movies, and I always feel sad, knowing that in real life, the horse could break its jaw or flip over backwards, potentially breaking its neck or spine. Take your tack off, people!! xDD
WOWIE THIS IS LONG!! xDD I hope I answered all your questions!! If you have more, just let me know : D I hope it all made sense and didn't bore you xDD