Ge 1:15 "and let them be for lights in the firmament of the heavens to give light on the earth"; and it was so.

16 Then God made two great lights: the greater light to rule the day, and the lesser light to rule the night. He made the stars also.

17 God set them in the firmament of the heavens to give light on the earth,

18 and to rule over the day and over the night, and to divide the light from the darkness. And God saw that it was good.

19 So the evening and the morning were the fourth day.

God made the sun, the moon and the stars and every other celestial bodies out there in outer space as servants of man.

They don't dictate or exert an influence as to what happens to a man's life so that if we study their positions we can somehow make a prediction of what will happen to our lives. No, they are servants.

First, they are placed there to help us establish a calendar.
Second, they are there to give us light.

Moses in these verses had to emphasize the functions of these celestial bodies to correct the common misconception back then that these celestial bodies are deities to be worshiped. Moses says: "No, they are our servants."

Are there other life forms residing in these celestial bodies? Based on the purpose stated here in these verses as to why these celestial bodies were made, we can definitely say that there are no life forms there. They were not created to support life of some other life forms out there.

Ge 1:14 Then God said, "Let there be lights in the firmament of the heavens to divide the day from the night; and let them be for signs and seasons, and for days and years;

"Lights" literally means light bearers or light holders or chandeliers in Hebrew. The sun, the moon and the stars? They are chandeliers or light holders in Hebrew. God made light to appear on the first day. Here on the fourth day, He made light holders. 

Ge 1:11 Then God said, "Let the earth bring forth grass, the herb that yields seed, and the fruit tree that yields fruit according to its kind, whose seed is in itself, on the earth"; and it was so.

12 And the earth brought forth grass, the herb that yields seed according to its kind, and the tree that yields fruit, whose seed is in itself according to its kind. And God saw that it was good.

Why did Moses mention only three types of plants here?

 God did create all others of course. But Moses is stressing only the plants that were primarily used by Israel as food for man and animals during their time. He wants to show that the vegetation that sustained man came from God. He created them. It was not some other deity that did it.  

Ge 1:9 Then God said, "Let the waters under the heavens be gathered together into one place, and let the dry land appear"; and it was so.

10 And God called the dry land Earth, and the gathering together of the waters He called Seas. And God saw that it was good.

Moses is teaching the Israelites that the gods of the earth and the seas that were worshiped by pagans were false gods. Their God was the one who created the earth and the seas. He is the true God.

The pre-flood earth was like a big island surrounded by bodies of water. The physical division of the earth into continents and islands must have occurred during Noah's Flood.

There were no rivers or lakes. There were only seas. During this time, a mist came out from the earth and watered it.

Ge 1:6  Then God said, "Let there be a firmament in the midst of the waters, and let it divide the waters from the waters."

7 Thus God made the firmament, and divided the waters which were under the firmament from the waters which were above the firmament; and it was so.

8 And God called the firmament Heaven. So the evening and the morning were the second day.

Moses here in writing to Israel these words wants Israel to learn that the God who created the sky and the waters was the God they promised to serve. No one else. Therefore to worship the god of the skies and the god of the waters as worshiped by the pagans during their time is folly.

The earth originally had a water canopy that enveloped it. This water canopy might be one of the sources of water during Noah's time that rained on the earth and flooded it.

Henry Morris enumerates the effects of the presence of a water canopy 

upon the earth. He suggests several effects of a vapor blanket.

i. It would serve as a global greenhouse, maintaining an essentially uniformly pleasant temperature all over the world.

ii. Without great temperature variations, there would be no significant winds, and the water-rain cycle could not form. There would be no rain as we know it today.

iii. There would be lush, tropical-like vegetation, all over the world, fed not by rain, but by a rich evaporation and condensation cycle, resulting in heavy dew or ground-fog.

iv. The vapor blanket would filter out ultraviolet radiation, cosmic rays, and other destructive energies bombarding the planet. These are known to be the cause of mutations, which decrease human longevity. Human and animal life spans would be greatly increased.

v. A vapor blanket would provide the necessary reservoir for a potential worldwide flood.

Ge 1:4 And God saw the light, that it was good; and God divided the light from the darkness.
5 God called the light Day, and the darkness He called Night. So the evening and the morning were the first day.

Why must there be light and darkness, day and night? God, in His wisdom, decided that man would be characterized by a period of activity and a period of inactivity.

Joh 9:4 "I must work the works of Him who sent Me while it is day; the night is coming when no one can work.

Daytime is work time. Night time is rest time. However, in the new heaven and the new earth, it is said that there will be no night there.

Re 22:5 There shall be no night there: They need no lamp nor light of the sun, for the Lord God gives them light. And they shall reign forever and ever

This is because, all who will be part of that new creation will be bustling with activity for God all the time, with their rejuvenated and resurrected and glorified bodies.

It appears that it was at this point that God formed the earth round. The expression "God divided the light from the darkness" seems to imply this. The division of light from darkness, day and night, is the result of the rotation of the spherical earth from the source of light.

It appears that the earth in its initial stage was not spherical. It was a fluid mass but it was not round to allow the division of light and darkness as we know today.

The expression "the evening and the morning were the first day" implies the 24-hour rotation of the now spherical earth with reference to the source of light.

The divine activity of the "first day" included the creation of the earth initially, light was made to appear and the division of light and darkness, day and night.