Why did he put Mizbechos to the Heavenly legion in the Chatzeros?
Malbim: The Mizbe'ach to Hashem was inside the Heichal. He made it seem that Hashem is like a king conducting matters inside, and the Heavenly legion runs matters outside.
Why did verse 4 say "Banah", and here it says "va'Yiven"?
Malbim: When the Vov switches future to past, it shows that the action was done repeatedly; it is close to present tense 1 . Building Mizbechos to Hashem inside did not complete his purpose. It was finished only when he built Mizbechos to the Heavenly legion.
What is his source for this? The Torah usually uses a Vov with future for past tense, including one-time matters such as birth, death and burial! (PF)