Yes, on the top and bottom faces, the grain is running in the x-direction. On the long edges, the grain should also be in the x-direction, but when you get to the bottom (where you've put the y-axis line) and the opposite end., the grain could be running anywhere, so you just need to follow the lines you see.

Within the cavities, it's normally a question of just using whatever direction works best (though try to keep with the grain in the neck pocket). You'll hardly be able to see in them, so achieving a perfectly smooth finish in them is only really for those with bad OCD. Most commercial guitars have pretty badly finished cavities as getting them smooth tales time, and time is money in guitar production. Which doesn't mean that you can't get them smooth if you really want to take the time. You might want to spend a bit more time smoothing the areas of the trem cavity that will be on show, but even still, it's not worth going overboard.