1: Flute = Darker tone, hard or soft tone, Low Whistle = softer tone (still dark though, depending on the maker), normally. Although, there is more variation with the flute than a whistle. With flute, you can get a dark or light tone, a soft or hard tone, loud or quite, more range in the octaves, etc. With the low whistle, those kinds of things are more set in stone, but not entirely. So yes, your guess is more or less correct.
2: About you holding your hands “wrong”, if you bought a silver concert flute, yes, you would have to change, but I’m pretty sure most Irish flute makers make flutes for “lefty” players. Although, normally, there’s a small fee.
3:Pros and Cons. Irish flutes (wooden, most common) crack. They also require regular maintenance such as swabbing, oiling, etc. So, I guess you could say with more benefits comes greater responsibility. Now, if you are good with your “regular maintenance”, it shouldn’t crack, but on the occasion, it does… and it sounds horrible… and it makes you want to cry. Flutes are also challenging for a beginner, mainly because one has to develop the embouchure. That normally takes a while, and can take even longer to really get how to change the sound and tone to how you want it, on the fly and consistently. As for the low whistle, the grip is harder, so if you have small hands, that can be a setback in itself. Some makers, though, make whistles specialized for small handed people, so hope is not lost. But over all, whistles are easier to play than flutes. Plus, they can take a beating. Whistlers joke about using their low whistle in a pub fight. Some of them probably aren’t joking though…
4: If you are financially minded, and do not want to spend that much money on the instrument, don’t even think about the flute world, unless you get one of the “affordable flutes”. The lowest that the decent keyless quality affordable flutes go, as far as I know, is about $275. Much lower, and you have a piece of crap. The average price for keyless flutes with the other stuff (tuning slide, for example) is about $800-$950ish, I think. Higher end flutes can be as high as $2000, normally with insane waiting lists. As for the low whistle, you can get a good quality whistle for about $150. They normally range from about $150 to $350 maybe. As you can see, they are much, much cheaper. Unless, of course, you count Copeland. I think there’s one of his whistles in the used instrument exchange is up for $1000. Maybe it’s sold, I don’t know. He’s not making whistles anymore BTW.
Anyway, hope that “essay” helped!