Guys like BigT will be able to help you more with this but I'll give my two cents...
If the weight is too light then the bar will travel up quicker than you'd like. In this case you probably just don't have to dip as low, but still make sure you're concentrating on pulling yourself under that bar as fast as possible. As the weight gets heavier, you won't be able to pull as high so you'll have no choice but to dip lower. Another thing, make sure that you're not doing an upright row. Your power should come from your legs driving your straight arms up then when you've reached the 'power shrug' portion of the lift, instead of bending the arms and rowing it, dive under it. If those elbows bend you've wasted the leg drive and are relying on arm and shoulder strength which is the reason why a lot of claimed 'cleaners' attribute shoulder problems to the movement.
As far as the elbows straight out thing during the catch, I have no idea and am working on this myself. My fingers can't possibly stay wrapped around the bar even a little bit if my elbows are out like that. Hopefully somebody else can help you (us) with that question.