Buy once and buy quality is a good mentality and can save you money in the long run. However, for a paddle I'd consider getting something a little cheaper first. Not because you may break an expensive paddle, but if you're new and may be having some swims, it's easy to lose your paddle! Also, you put a lot more support strokes etc. in when you're learning, and this can scratch up and significantly reduce the life of your blades if they are hitting a lot of rocks.
Also, paddles do end up breaking. If you get a cheap one first to learn a bit on, then upgrade, you'll always have a spare sitting at home!
This isn't to say you shouldn't spend more getting something good, I just want you to think about these points before you buy. If you are still happy to spend the money then go for it! You won't be disappointed.
As for what to buy, if you're keen to get a werner, there's a fitment calculator on their website. You fill in the answers and it recommends the type of paddle and the size. You mentioned sea kayaking. Generally in sea kayaking you're paddle will be a bit longer, and the blades will be offset near 90degrees. In whitewater kayaking the paddles are generally a bit shorter, I guess because you're more likely to hit a rock with the blade with a longer paddle. This can bring in issues like shoulder dislocations etc. Also if you're doing play boating especially, the length is smaller, and the feather on the blades is either 0, or close to 0 so that there is no resistance from the none power blade when you are upside down and both blades are in the water. The feather on creek boat paddles is usually around 45degree's.