1. The Kikigaki commentary says that "one holding is one releasing" (i.e., these actions are identical).  Perhaps one can understand this as "holding the one is releasing the other" in the sense that holding one implies not doing evil, while releasing the other implies dedicating oneself to good practices. 

2. "Before the first move" refers to anticipating the opponent's next move in military strategy or games of chess and then moving one step ahead of what the opponent had intended to do next -- in other words,  seizing the initiative before something important is about to occur. 

"Eight or nine (moves) completed" alludes to the following Zen dialogue, which Dôgen quotes in full below, attributed to Caoshan Benji (Sôzan Honjaku, 840-901): 

Caoshan questioned Elder De (Toku), "'The buddha's true dharma body  resembles empty space; responding to creatures it appears in physical form  like the moon reflected in water.'  Now, how do you explain this principle of responsiveness?"
De replied, "It is like the donkey spies on the well."
Caoshan said, "Your statement is a great statement, but it only states eight or nine [parts] complete."
De said, "Master, then, what about it?"
Caoshan replied, "It is like the well spies on the donkey."

Regarding this dialog, note that the word for "donkey" actually is a copyist error for the word "pulley"; in other words, the pulley used for drawing water out of the well points down (looks down) into the well, while the well reflects (looks) back; in short, they stand in relative relationship to each other. 

3. Regarding the relationship between "buddha seeds sprout in accordance with conditions" and "conditions sprout in accordance with buddha seeds," note that the pattern of reversing statements so that "A-verb-B" becomes the same as "B-verb-A" is quite common in Japanese Buddhism.  Interpreted in light of a mandala's visual depiction of the entire universe as an outward projection of buddha, Dôgen's statement merely asserts the obvious:  the phenomenal world of causes, which leads humans to buddhahood, is itself a projection (or result) of buddha. 

4. According to the Kikigaki commentary, suns and moons should be interpreted as "this and that."

5. Nature, aspect, embodiment" (etc.) each constitute one of the "ten suchlike" features of reality, from a famous passage in chapter two of the Lotus Sutra.