I love that you brought these topics up since I was gonna write a devlog about mechanics today :) I've been struggling trying to find out how to make the most intuitive mechanics that will make sense/be consistent in any scenario
For example, about the crystals and not knowing which one goes first- if I do change it to where there is an even number of spaces in between, I will still eventually need to account for what happens when there's an odd-numbered space in between, since that can happen based on what the player does. For those cases, I just made a priority system where crystals go first depending on the direction they're going in. So top priority is upward, then right, down, and left.
The other thing you mentioned was crystals splitting- I have to keep in mind that any number of crystals could enter it, up to 8. In the interest of consistency, I decided everything would only split into 2 halves. If a crystal is odd-numbered, then its larger half will go up or right, depending on the direction it entered the splitter.
Now that you know where my head is at, I'm curious to hear what you think! I appreciate your thoughtful comment :)