The correct length and angle are vital to the selection of your ideal paddle. In years gone by it was suggested that the correct length was discovered by reaching up and curling your fingers over the top of the paddle. This would imply that a six foot (2m), man paddling an Eskimo Topolino would use the same paddle in a sea kayak. This should not the case.
Paddle lengths are far more related to your boat length rather than your height. A short boat in the region of 2.5 m would use a paddle between 180 to 200cm ideally . A 3.5 to 4.00m touring kayak somewhere between 200 and 212cm. Longer touring and racing kayaks use 212 to 260cm.
Obviously if you are a huge sausage munching savage from Bavaria , you will tend towards the longer lengths in the range and if your Nepalese river guide feeding on rice and chai you'll be a shorter paddle length paddler.
Your paddling requirements play an important part in your paddle length selection. If your paddling tends to involve short blasts of high stroke rates for acceleration, such as polo, ocean surfing and technical creek boating you will best look at a shorter paddle length. By comparison paddling at a constant speed and retaining your momentum in such disciplines as sea kayaking, marathon and sprint racing and general touring you'd focus your attentions on a paddle length that may feel cumbersion to accelerate, but will keep you going along nicely. Somewhere in the mid ground are those paddling pursuits that require the occasional rapid acceleration, times of top speed and nimble paddle strokes to maneuver the kayak through difficult water or in playboating features. Disciplines such as freestyle, slalom and white water river running all require mid length paddles, although the current freestyle momentum is for short paddles in order to keep pace with the very shorter boats and their quick tricks.
Angles are a a funny subject. Back in Greenland, Eskimos used to escape certain death in storms by paddling head on into the wind to avoid being blown over or broached by waves in their touring shape kayaks. It was essential in these conditions to have one of your blades feathered in order to paddle into the wind successfully. By and large most of us don’t hunt polar bears and seals from our kayaks any more and the thoughts of being out in storm does not fill us with glee!!
So why do we feather our paddles!! Who knows, possibly a force of habit mostly. However going for lower feather angles is definitely better for your wrists, where something like 45° degrees definitely does have an advantage in windy conditions. I prefer 60° degrees but then I am old and set in my ways and have had several lifetimes of competitive paddling.
Competitive paddlers still have high feather angles to reduce wind resistance, and polo players need to deflect the ball forwards predictably so these guys will always cling to the higher angles. My advise is , if you don't need it, be nice to your wrists and lower your angle, it costs nothing extra. But remember once you lower your feather angle, you will find it a little difficult to return back to a higher feathered blade angle, at the least a few missed strokes and at worst, wrist strain.