The short answer to your question "was manna physical or spiritual?" is - Yes.
God provided the Israelites both physical and spiritual sustenance. And today, God still provides us the spiritual food that we need in Jesus (John 6: 32-35)
From the Exodus onward the idea of Manna takes on largely spiritual meaning in the mind of both Jews and Christians.
For instance, if we allow "text to interpret text," we can look at Paul's statement in 1 Corinthians 10:2-4:
"They were all baptized into Moses in the cloud and in the sea. They all ate the same spiritual food and drank the same spiritual drink; for they drank from the spiritual rock that accompanied them, and that rock was Christ"
The word manna comes from the Hebrew words (מן) man "what is" and (הוא) hu "it" -
"what is it?" This is the question the Israelites asked in Exodus 16:15.
According to the Anchor Bible Dictionary (vol. 4/K-N, pg. 511) - the Manna has been associated with a natural phenomenon that occurs in the Sinai and a gum resin that is produced by a number of plants such as the Tamarisk Gallica
Based on Moses telling Aaron to place Manna in a jar (Ex. 16:32):
So Moses said to Aaron, “Take a jar and put an omer of manna in it. Then place it before the Lord to be kept for the generations to come.”
a Jewish legend came about that this Manna which was hidden away will not be found until the arrival of the Messiah (2 Apoc. Baruch 29:8) and also in (2 Maccabees 2: 4-8).
The book of Revelation reflects this idea - in the letter to Pergamum (Rev. 2:17) - John writes:
Whoever has ears, let them hear what the Spirit says to the churches. To the one who is victorious, I will give some of the hidden manna.
Essentially - if the "hidden manna" is now available - then the Messiah is here.
As far as the description of Biblical cosmology and where the manna comes from:
To the ancient mind - particularly the Jewish mind - God is always up and any gift from God comes from above (we think this way as well when we describe which direction heaven or hell is). So the biblical language is probably more metaphorical than literal when describing the direction that the manna comes from.
For instance - whenever someone is moving toward Jerusalem in the New Testament - the direction is always "up." If you are heading away from Jerusalem (like to Egypt) you are going "down." Today, we use "up" to describe driving north and "down" to describe heading south - "I'm heading down to the Florida keys for a vacation and then back up to New York in two weeks."