1. Try not to go beyond 18 billion people. Otherwise the planet starts getting really crowded and people get really angry.
2. Smaller ships don't do well against larger ships, unless the smaller ships have fleet support modules (ships with those modules equiped tend to draw fire) or superior weapons and defense (huge number advantage works). Assuming both sides have equal weapons and defense, a large ship can ussually take a beating, while returning fire that will probally kill a few smaller ships, thus reducing firepower that can be used against it next round.
5. Consider it something to be used as part of an advanced strategy. Since you are new to this game, you should avoid it for now. By then you can probally figure out if its worth it. That said, some civs like the Arceans get their "Weather Control Zenith", a planet improvement that increases a planet's quality.
6. Good tends to get screwed over in most random events. The bonuses can be significant enough that you may wish to avoid researching "Xeno Ethics". By the way, researching "Xeno Ethics" prevents further random events, so research it early if you plan on playing good, or later if you plan on playing evil.
7. I think you are talking about the "ship quality" bonus. Its a bonus that is applied to all ships built by that planet. The "ship quality" bonus increases ships weapons and defense by a the given percent. Other bonus types include "ship HP" (increases ship HP by percent ammount) and "ship speed" (increases a ship's speed the number given).
Planet improvements that give these bonuses includes, but not limited to: the Arcean "Stellar Forge" which proivdes both a ship quality and ship HP bonus, the Drath/Altarian "Doomsday Generator" which provides a very large bonus to ship HP.
If you want more information, check out the guide I wrote. Though its was written for those who already knew how to play DA, so feel free to ask questions.TA 101