With the arrow nocked and on the rest, take another arrow (or better yet a bare shaft) and hold it against the inside of the riser, next to the arrow on the rest. These two arrows should be parallel with each other. Since the entire bow is assembled to the machined riser, everything should be square in relationship to the riser. The bare shaft held against the inside of the riser serves as a straight edge, and serves as a reference point for finding correct center shot. The arrow’s final resting place will be dead square to, or slightly away from the riser. I have yet to see a properly tuned bow that had the arrow lined up inside of square.
This is basic centershot rest adjustment. Fine-tuning will likely be needed, but this is the best and fastest method I am aware of to set initial rest position.
As for where to cross the cables, take them out of the cable slide and let them cross naturally. If they cross above, then have them that way when back in the slide. If below, then below.