So God is the top, I imagine because he's based on the biblical God, he must be the creator of the universe/multiverse of the verse.
Yeah, The Nightside follows a very strange version of the Bible, where it's less literal and more parable. Lilith actually flat out says that to explain why she's so powerful, Eden was just a parable when reality and the Universe were much less screwed down than they were in the future.
For example, John and co go back in time several times in Paths Not Taken and to reach the time when the Nightside was made, John had to go countless years back to when Time and the laws of reality were less fixed and talks about the ancient Monsters in the forest, before they were bound by Human understanding.
If you're wondering, Time is circular in the Nightside series, so the events which happened after your Time travel already happened, for example, they go back in time 3 times, once to the fall of Camelot and the decline of the Roman Empire, then further back to the Height of the Roman empire and then lastly to the unfixed time. The first time he goes back a Doorman remembers him from 300 years in his (the Doorman's) past despite John not having yet gone that far back.
It does introduce the Boot strap paradox, like when John gives Lilith the idea to name the Nightside, the Nightside, so it begs the question "who came up with the name originally".
Lilith seems quite powerful.
She's probably the most powerful being we've seen on the page. Closest to her is probably the Walking Man
Are the angels powerful too?
Extremely. Angels show up in the Second book looking for an artifact, and despite the Nightside being absolutely cracked in terms of its offensive power and what they can do, they were losing to the Angels of Above and Below.
Thing was too, those angels were significantly weakened when entering the Nightside.
Are there archangels as well? For example, Archangel Michael or Gabriel.
There is "Gabriel", but he's not an Archangel, there aren't really any classifications of Angels, just "Angels".
The reason being is that these are Old school Angels, they're Messengers of God's judgement. "Spiritual SS" as Suzie puts it. They aren't men in gowns and harps, they're who you send when you want the first born of a generation kill or a city turn to ash.
Gabriel kinda shows up, but it's technically not really Gabriel. He and Baphomet show up but state they got their names and forms by taking images from John's and Suzie's head and that they don't really look like that.