Earth is alive and kicking. The idea behind the colonization project was to not keep all the eggs in 1 basket. During Space War I, the Zentradi nearly wiped out all of humanity. To be sure that something like that would never happen again, it was decided to spread out amongst the stars and colonize worlds so that humanity would never die out. This is mentioned in SDFM.
There are shipyards in and above Earth (as well as in the Sol System) as well as the Factory Satellite (see SDFM).
Of course. You should see the defense network around Earth (M+).
The Galaxy Network (See M7).
Zolans, Protodevlin, etc. We've only had 3 series that covered new and strange lifeforms.
Your answers and many more can be found by watching the previous series.