For Ranma, I think it's a combination of being a straight man as a result of how he developed over the course of his life and being in and from a culture that has certain expectations when one lives by a code of ethics and conduct. From my own observations, he's clearly uncomfortable with the idea of being with a man, whether he's a guy or a girl. He also shows attraction to girls whether he's a girl or a guy. And while he's normally unaffected by his curse despite his empty grumblings (empty because he deals with it to the extent that he waits for cures to come to him instead of the other way around), partly evidenced by the many whys and hows of when he acts and/or dresses like a girl, he usually reserves his strong protests for when people put into question or insult something about him that he doesn't want others to judge him negatively about. I don't think it would be impossible for Ranma to ever like a guy romantically or sexually, but I believe that the circumstances would have to be really, really different from what we're familiar with for that to happen.
As for the physical and mental influences of the curses, by and large I think people look into it far too deeply than necessary. Takahashi ignores a lot of common sense things regarding physics for the sake of comedy, and that's why she didn't bog the story down with technical and realistic reasons for why cursed individuals handle themselves the way that they do. However, I'd like to point out that it's an assumption to think that Ryoga, Shampoo and Mousse were convenienced by Jusenkyo, considering that there's no telling how much time they had to get accustomed to their cursed forms before they made their (re)appearances, which isn't helped by the fact that time doesn't exactly flow realistically in the series.
And while I'm no expert on panda bear anatomy, I don't think it's a stretch to think that at least Ranma wouldn't have any real trouble adjusting to his cursed form. It's not like balancing on legs are new, and he's still human, so it's not like it can be compared to where a baby human would have to start, both in terms of experience and physical development. It's also not like he suffered a serious injury or brain trauma, where he'd need therapy to relearn how to do things from scratch.
But what I'd really like to address is the sense of balance. Between the two sexes, the vital parts (like the brain, eyes and vestibular system) that it relies upon don't change significantly, while the other parts (such as the skeleton and muscles) are relatively easy to adjust to once you put your mind to the task. After all, the main issue is that you're still balancing on two legs, not four, or a snake body. It's not alien. Going back to the car analogy, the biggest issue would be getting used to the size, shape and weight distribution of the car relative to what you're used to driving, as you are still perfectly able to drive on the roads. For instance, my sister recently had to use our mother's car instead of her own, and my mother's car is nearly twice the size of my sister's. Aside from that, there were a lot of small differences, such as where certain things were located and how the car performed (including going from front-wheel drive to rear). But she was able to go about her business just fine, except that a few days in she misjudged a turn and scraped the side of a curb. Ranma made the same mistake with Mousse after getting herself around just fine. I think it can also relate to my experience with a bike, because despite having not ridden one in a decade (thus going from a young teen to a full-grown adult), as well as riding a different kind (in terms of size, and having speed options and the brakes on the handles), I was still able to ride it without any compromising problems.
More to the point, though, is that Ranma and the others aren't exactly normal people, and can't be held to the expectations of our standards as such. They perform many feats that we couldn't possibly do with casual effort, which -- to me -- suggests that we're barking up the wrong tree trying to rationalize the hows and whys in terms of handling their cursed forms. That's not to say that Jusenkyo may not have some of the effects suggested, but I'd be prudent when it comes to assuming what any particular spring does; and they would be assumptions because we're never told straight-up how things work. For instance, "young girl" literally means just that, a female that is of a young age. Assuming that there's anything beyond the physical about it is sending Occam's Razor off on a train, because young girls can differ in their sexuality, gender identity, personality, the kind of gestures they use, the interests they have, and they don't even need to be from a different culture to achieve such differences. Personally, I just can't believe that the spring would favor a single combination of those, or choose a combination at random. And seeing as Ranma still seems to be Ranma in either form, he didn't become his own idea of how a young girl would be in that regard, either.
That said, I think it's fine to speculate and exercise one's creativity in a story, in regard to these matters, but I'd personally exercise some caution. I would even suggest to not take any of my own assertions seriously, since my guesses and reasonings shouldn't be any better than anyone else's. I was just tired, hungry, bored and I was struck by a whim. ;/






