1. Although all English translations render this as God walking (hlk), the hithpael participle may go with 'the sound of God in the garden' instead; i.e., the couple heard the sound of God's presence drifting about in the Garden. The two readings amount to the same thing but, as a matter of exegetical integrity, the distinction should be noted. A similar form of this root (but in a different stem) appears in 2:14 where it describes the flow of the river Tigris.
2. "Where are you with Jesus, brother?" is a question we need, especially, to ask our members in the church often. It is a pointed but genuine way of caring for our brothers and sisters in the faith.