Bending an axle flange is a fluke, it doesn't happen very often, and you usually have no idea when it happened.......unless you're in an accident and slam the wheel into a curb or something. I wouldn't worry about it happening again. You can replace the axle shaft and go on, then learn some more so you have some kind of clue what you're talking about and consider changing to a stronger axle after you've learned (a lot) more.
BTW, the axle is either held into the housing with a retainer plate at the outer end of the housing, or by a c-clip at the tip of the axle shaft inside of the center section (inside the gears). It's much easier to replace a non-c-clip axle, because you don't have to take the cover off the diff.
Spline count has nothing to do with gearing or power, it simply means the axle shaft is bigger and stronger. D35's have 27 spline axles, early 8.25's have 27 spline axles, later (97' up) 8.25's have 29 splines, d44's have 30 splines, Ford 8.8's have 31 splines.