Well i would concentrate more on learning the proper movements in the swing, hips start first in the downswing, this will really set up the rest of the swing.
If done correctly, yes everything is slowing down before impact, even for most people the clubhead is slighly slowing down, which is OK, its close enough to maximum velocity that you wont notice its
The reason why is, the kinetic chain is a polynomial, meaning it has a peak for maximum velocity. If you try to time that peak, you'll end up just before or just after it, and maybe at the peak some of the time. That means, your going to be hitting with nearly the same velocity every time, because that velocity exists twice on the curve
Lets say you have three potential timing spots for clubhead velocity, just to simplify, 110mph, 115mph, 110 mph, that would signify three spots on the curve; before max, max, after max. So if your timing is good, your clubhead speed will always be 110 or above, and that is consistent. For amateurs, we tend to really loose power, lets say swing at 80 mph, but our max might be 95-100 mph. So were not swinging in a +/- 2.5 mph range, but a +/- 10 mph range. For us that is when you hear, "Oh i really caught that one", well you happen to time it just right that time :p
The reason why the the muscles are slowing down, is because we are BiSymmetrical down our midline. So when our rotation passes our midline, the other side wants to counter this. This is why weight forward is a big key. If your weight is 50/50 at impact, your midline is way to far behind the ball, and your expending your energy way before the ball. If you get your weight forward, your midline shifts forward, delaying the slowdown till the optimal time, allowing the clubhead to reach near max velocity.