Um yeah um

This isn't Starcraft really.

It really comes down to what map type, what you plan on doing, what your enemy is doing.

Colonizer Capital ships are a good use of your free capital ship but I and some others prefer a more aggressive approach and go for a Carrier Capital ship plus a Colonizer Frigate. Sometimes a small forces you to go aggressive whereas a big map or easy AI you can go Colonizer Capital ship. After that its a bit in the air.

Depends on your strategy. Civilian is obviously economy and you do need at least two of those to get the hostile/artic planet research done. Trade Ports are an obvious must but when you get them is also map dependent. Too soon on a small map and you can be overrun, too late on a big map can cause the same thing. With Military, Corvettes (I am assuming you are talking about Rebellion version) are a must with a Titan down the line. Depending on what faction you might want to focus on Armor (TEC) or Shields (Advent) to improve upon. After that it gets murky.