1: There are several ways to deal with raiders. STOs will defend colonies if the raiders ever show up on top of them and are also a good way to defend orbital miners and Sorium harvesters. For proper colonial defence you should probably have ships as the raiders could attack shipping inside a system. If you want to counter a raider ship you make sure your active sensor is tuned in to around 1000 tons target signature. Depending on your techlevel you might be able to outspeed and outrange the raider. In that case you simply need a small ship that can “kite” the raider and kill it from outside the raiders weapons range. If you can’t do that then a military ship of around 10k tons should easily dispatch a raider if they meet in a fight. The raider spends a lot of tonnage on staying stealthy, so you should be able to win in a ton for ton fight.
2: I reccomend looking at AARs for inspiration or the Aurora discord server which has a chat room just for designs.
3: From what I have experienced you dont need to make a very complex order of battle for your ground forces. Maybe as low as 2-3 levels of organization will probably be enough in most cases. For assaulting enemy fortifyed colonies you might want to bring armoured units that the enemy will strugle to penetrate. When invading a hostile one of the biggest issues might be troop lift capacity, therefor an “elite” force should be assembled for the assault as lower tier units will not do as well ton for ton.
This is an example of a division of tanks. I have not bothered adding artillery which I probably should, but this division could probably take on most colonies that are lightly defended.
4: There are several reasons to colonize even without the precence of minerals. One reason is you get more population growth, as smaller colonies have higher growth percentage. If population is not an issue then it is still good to spread out for some of the reasons you have stated. If you have a colony with a lot of finacial centers but no govenor bonus for wealth creation on the same colony you are missing out on free wealth. Therefor it is good to have specialied colonies.
It is also good to have colonies in different systems to lay claim to them if you have neutral/friendly relations with an NPR.
I also like having small colonies in most systems to have refueling hubs and maintance locations to keep pushing the range of my exploration ships. You can also do this with maintance ships and such, but it is not the way I like to play. And sometimes I set up small colonies in between imporant systems to make sure my civilan trafic is not gonna be ambushed by raiders.
5: I have never tried them so someone else will need to reply.
6: Keep going with the trial and error. If you like youtube, then Defran has made many good tutorials for various things about the game, aswell as some older playthrougs which should mostly still be relevant. Other than that ask like you have just done if you wonder about anything as this community is very helpful.
7: Aurora v1.0.0 Launch Documentation - #35 by AuroraSteve It is a bit much to write here so you can read the patch note if you want. Most should still be relevant with minor changes since.
English is not my native language so forgive my for any misspelling and hope this was somewhat helpful 