Unfortunately this little exercise took much longer to do than I wanted, mainly due to workflow problems. For example, I know that you like to do your blocking with linear keys so that you can get an idea for the timing, but I find that I have trouble getting a good feel for it without a good number of breakdowns to establish the spacing. Is that something that you just pick up over time, or do you need to put in breakdowns? I don't want to spend a lot of time putting in breakdowns and trying to establish my spacing before I get my timing locked down because then I feel like I waste a lot of time moving keys around. Do you like to get the timing right on your extremes, then start putting in breakdowns to determine the spacing, or do you try to set up spacing and basic arcs before moving on to getting the timing locked in? I know that timing and spacing are closely connected and it's a constant back and forth, but I feel as though I can reduce the amount of back and forth between fixing one thing, then back to the other, then back again kind of working. I hope all that made sense.
those are great questions. First, let's look at the obstacle course. Overall it's working really great. The only part that sticks out as being a bit weird is the very end, after the x147 area. After the ball goes through that C curve half loop it goes up but doesn't finish its momentum, the hang time gets suddenly cut off. Look at your spacing, how the ball goes up and then stops at x148, as if it hit an invisible wall. Keep going up until the momentum dies down.
Same thing for the x167 area, the up movement comes to a halt too quickly; and the same thing for the subsequent back and forth. They all kinda stop too quickly. The overall back and forth though is taking a bit too long. It's not a huge thing, but as I'm watching it, I'm thinking, okayyy, this ball really doesn't want to stop rolling. :)
So, the sudden stops and the overall length of the back and forth are the things that stand out the most and need fixing.
Now, in terms of workflow.
It's okay to have a lot of breakdowns when you block out a shot. Some movements need almost no keys, others you might have to go in there frame by frame in order to sell the idea. The point of blocking is to show every idea that you have clearly, so that the audience doesn't have to guess. If you need more keys to sell an idea, then so be it. The moment the idea is clear, move on. If you don't, then you're going into polish land which is too much at this point.
Spacing and timing go hand in hand, at least that's my take on it. The spacing will determine the timing. If you space out a head turn evenly, then the timing is even and the head turn boring. But if your spacing is big at the beginning and then suddenly small for the turn, then the timing will be more like a take or a feeling of a faster, surprised, shocked, determined, etc. head turn.
I do though, like you said, worry about the extremes first, or at least the major points and beats the characters will hit and go through. Then I add in break downs where it is needed in order to sell the story point or action. But you do get used to that process over time to a point where you will need fewer breakdowns. But again, it all depends on the action. Some things just need more breakdowns.
I hope that makes sense. :)