I'm a newbie too, is there a way to select which race you want to play as in the single player scenarios? I couldn't find this.
Yes, there are a few buttons for each Player/AI in the load out screen. I am at work at the moment so this is off the top of my head, the first changes race the second is for the AI to control the it's play style (Aggressive, Explorer, etc). I hope that helps.
Defences are great, and work a treat for keeping pirate attacks a bay. The planetary defence cannon is great for killing siege frigates that come in close to the planet while the Defence Hangar takes care of the rest of the enemy.
Trade ports give 1 credit per second once built. There is also a bonus for the longest route, that is, each planet that contains a trade port between the two furthest points in and unbroken path within your controlled space will be worth 0.075 to income. So if there are 5 trade ports along the route you will earn 1.375 at each trade port or 6.975 overall per tick, thats almost 2 free trade ports! Also note that if an enemy destroys a trade shit they will recieve 50 credits, these will auto respawn after 25 seconds.
More detailsRefinery's are another story, each faction use these differently. A refinery is based on your resources on planets you own one jump away. The TEC Orbital Refineries for example adds 0.06 to metal/ore income if they are player owned points or 0.08 to captured netural extractors.
Here for more infoWow thats a lot to learn, http://www.soasewiki.com is a really useful resource!