What do host means here?
Thus the heavens and the earth and all the host of them were finished by the Lord of hosts.
What does host mean?
Thus the heavens and the earth and all the stars, the sun and the moon were finished by the Lord of armies.
Isn't it funny how the word host can assume different meanings? Let me put it this way, the "host of heaven" has two meanings, the first one is celestial bodies (the sun, moon, stars and angels are referred to as the host of heaven) and it could also be reference to evil angels.
Host is also "an army" in archaic English.
Hosts in Bible can be "Army", in Portuguese the name "LORD of Hosts" is "SENHOR dos Exércitos", because He created all creatures, even the celestials. The king David has called God by this name many times, to give Him glory and to show that it was not his army who defended him, but God Himself did it.
See PSalm 24.10
I think you are confused for the using of the word "thus". Probably the author said something before this phrase to make sense, 'cause "thus" is a consequence conjunction. So, this phrase show us the consequence of the previous sentence. "Therefore", "hence" and "thus" are similar words.