Happy new years all, enjoy!
Scattered Big Dipper, Luminous Venus: The characters used for Venus are a more ancient way of addressing it. I would treat this just as names for Lu Muxian's attacks with a star/planet/astrology flair. If you wanna read further into it, the specific characters used does match with that from an old poem. However this specific line within it doesn't mean too much other than the sky being clear and the Big Dipper and Venus being prominent.
Awakening of insects: This is from the traditional Chinese lunisolar calendar which splits the year into 24 periods. This refers to the 3rd term starting in 5-6 March which corresponds to when Spring starts. She's basically saying the time period isn't right for snakes to be around.