I’ll give some answers, from the perspective of someone who really likes mounted combat. I’m sure some other people will answer from the other perspective. :)
To begin, everyone hates it at first. And yes, combat mainly involves riding in huge circles. In towns, you need to either walk or canter slowly to avoid bumping into stuff. Many people, even me, will change to a standard mount if there is a lot of in-town maneuvering to do. Though I like mounted combat, I absolutely am a klutz in towns.
If you are bumping into things because your graphics and the game aren’t synching up with where you really are (you suddenly rubberband and you are face-planted in a wall), that’s a graphics issue to some degree. I finally sorted that problem out, and yet in some areas where the game lags, it still happens.
Now to your question:
1. Good news: once you leave Rohan, there aren’t a lot of things designed to be fought as mounted combat. Of those that are, many people just do it on foot anyway.
2. There’s a difference in steeds. It’s not obvious at first, but you already have access to all three by using the drop down menu at the top of your mount’s trait page. Light steeds are more maneuverable on turns, and heavy steeds are not, but they are a little sturdier. If you run medium or heavy, use legacies and traits to increase agility so you get more tight turns. There are other skill differences, so sure try them all out, but here’s the thing about bridles: The major legacies are specific to that type of mount’s skills. The minor skills are more generic and apply to any type of mount. You won’t want to have two bridles, so figure out early on what you like and stick with it. But in terms of trying out the types, just use your one bridle, that’s probably enough for you to figure out which weight you like. Also, keep switching to higher bridles … the first bridle they issue you is pretty awful. The fury contribution will increase a lot with higher levels. You will hear people say fury doesn’t work, but what they are talking about is the lack of satisfying scaling at the cap level, it’s still useful in Rohan and Gondor.
3. The real thing to learn with mounts is how to use the three stances … as a minnie, for instance, I cycle back and forth between red and blue continuously. My cappy likes yellow and red. So, play with those a lot, changing on the fly. Rohan’s landscapes are huge because you need large fields for mounted combat, so take advantage now. Don’t try to use it in forests. The training track is okay, but you will probably feel better out in the open. Use your fury contribution to its best advantage.
I actually use my mounted skills even when the game doesn’t dictate it (my burg gets mounted stealth everywhere, and my minnie has really good heals on a warsteed).
I think the main thing that turns people off about mounted combat is that it takes patience. There are no huge dps bursts where you just flatten stuff. After soloing for 75 levels, that’s hard to adjust to. But if you change that mindset and come at it from a different perspective, it’s fun to figure out.